托福机经2025:7月19日（下午场）托福写作机经是什么(含试题

阅读

听力

　主题：stone block是不是Olmec writing

　　No similar objects

　　First, the stone block is the only Olmec object that appears to bear signs of writing. When a culture develops writing, the writing appears repeatedly on many objects. But, while many other stone blocks have been found at Olmec sites, none of them have similar markings. This suggests that the markings on the recently found block do not represent a writing system.

　　First, it's true that it's the only Olmec object that contains writing. But remember that stone objects can experience significant weather damage. The weathering effects of humidity, rain, and other factors will often erase any written inscriptions, especially on objects that are more than two thousand years old. Our Olmec block may be a rare example of an object that somehow avoided these weathering effects. Maybe the stone was buried in a type of soil that protected it from damage. In other words, many other Olmec stone blocks may have originally contained inscriptions, but on most of them the inscriptions have been erased by weathering. But since this block may have been protected by a special type of soil, it has avoided damage and its inscription has survived.

　　Signs may be decorative

　　Second, the signs on the block may have a different purpose than writing. Many of the signs look similar to designs and shapes found on ancient Olmec artwork such as figurines and masks. The designs on Olmec artwork are decorative or perhaps have religious symbolism but are clearly not written language. The similarities of the signs on the discovered block to decorative or religious designs suggest that the block may simply be an example of Olmec art and not evidence of an Olmec writing system.

　　Second, the markings probably do represent writing and not just artistic designs or decorations. When you look at how the signs on the block are arranged, you'll find that the arrangement is typical of written language, but not of artistic designs. The signs on the block are arranged in separate groups. Such groups may represent words or sentences. Also, some signs are repeated several times, just like some syllable or words are repeated and written texts. Ordering signs in groups and repeating signs are typical of writing. Decorative designs are not arranged in that way.

　　Origin

　　Finally, the discovered stone block may not even date from the Olmec times. Archaeologists generally date ancient objects by examining their original position in the ground. However, the block was found and dug up by local road workers who simply put the block in a large pile of other materials before noticing its historical value. Since archeologists were unable to observe the block's position in the ground, establishing the block's true date and origin is difficult.

　　Finally, scientists did find a way to date the block. You see some ancient pottery was found next to the block. Ancient pottery can be dated based on its style, its shapes, its decorations, etc. The pottery found at the site had a very specific style that clearly shows that it was made during the olmec period. Since the pottery and the stone block were found together, we can be confident the block dates to the Olmec period, too.

阅读

听力

　主题：min min light的成因

　　First, it is possible that the Min Min lights are caused by bioluminescent organisms. Bioluminescent organisms produce chemicals that generate light. One hypothesis about the Min Min lights is that they are caused by swarms of bioluminescent insects that travel across the landscape at night and emit light as they fly.

　　First, it's unlikely that the men lights are created by bioluminescent insects. For one thing, the min lights are very bright. But the light emitted by bioluminescent insects is normally very dim, and we. So it's doubtful that any swarm of insects would admit enough light to account for the brightman. Besides the minimum, lights are usually described as circular discs of light. Whereas bioluminescent insects. Are not known to fly together in circular formations.

　　A second theory is that the Min Min lights are caused by the release of naturally occurring gases from the ground. Other mysterious lights similar to the Min Min have long been noted around the world. Most of those other lights have been found to be the result of ground gases, particularly methane gas. As methane and other gases chemically react with oxygen in the atmosphere, they ignite and produce light.

　　Second, it's unlikely that the min min lights are caused by gases released from the ground. You see, methane, the ground gas that's known to produce light in certain parts of the world, is formed from decaying organisms usually found in what lands. Wetlands are areas where the ground contains a lot of water. However, the main lights have been spotted in relatively dry areas far away from any kind of wetland. If the midland lights were created by methane, we would expect to see them closer to wetlands.

　　Finally, the Min Min lights may be caused by special atmospheric conditions. A warm layer of air in the atmosphere can sometimes act as a reflecting mirror. This layer of air can reflect distant light sources—for example, bright electric headlights used by automobiles—so they appear as mysterious lights floating above the horizon. The area of eastern Australia in which the Min Min lights are seen often has the correct atmospheric conditions for this type of reflection to occur.

　　Finally, the reflection theory might explain, well, the men men's sightings that are reported today but it has a harder time explaining the men men's sightings that took place hundreds of years ago. As you read, this theory explains the min min lights as a reflection of very bright sources of light. Like powerful electric headlines, for example. Bright electric lights may be common today, but as you've read in the passage, bright midland lights have been observed for hundreds of years. Long before electric lights even existed. Before electricity, light sources were generally weaker. It's daffle that the atmospheric reflection of those weaker light sources could have caused the men lights.

阅读

听力

　主题：40 年前 yellow legged Mountain frog数量 decline 的原因

　　Nonnative Trout

　　Some researchers have suggested that the problem is the introduction of trout (a species of fish) into water sources in the Sierra Nevada mountains. The trout were introduced to encourage recreational fishing, but they may be causing the frog decline. Trout are predatory fish that can feed on tadpoles (young frogs). Since trout are not native to the region, yellow-legged mountain frog tadpoles have not developed any defensive behaviors that would protect them from the trout.

　　The problem with the first theory is that people who enjoy recreational fishing started stalking the streams and lakes in the sierra nevada mountains with trout over a hundred years ago. As a matter of fact, it wasn't an easy thing to do at that time. The trout had to be carried into the mountains, in buckets of water, on horseback or on mule. But the interest in trout fishing was strong, and so the trout were introduced into many locations. However, the decline of the yellow leg mountain frogs didn't start until about forty years ago. So, the timing of the two events. The introduction of the trout on one hand and the frog decline on the other doesn't seem to match.

　　Pesticides

　　Others believe that chemical pesticides sprayed onto farm fields could be poisoning frog habitats and harming frog populations. To the west of the Sierra Nevada mountains lies California's Central Valley, a region with some of the most intensive agriculture in the United States. Pesticide use in the Central Valley is heavy, and it is possible that some amount of the pesticide contaminates the freshwater habitats of the yellow-legged frog.

　　The problem with a second theory is geography. Usually in cases of pesticide contamination, you have rain, water, washing pesticides off the fields, and then flowing downhill into rivers or lakes nearby. But the sierra nevada mountains are not only quite far from the farms in the central valley. Over a hundred kilometers. But they're also located higher than the fields in the valley. Since water cannot run uphill. It's not easy to see how the pesticides used in the central valley could get to the lakes and streams of the sierra nevada.

　　Fungal Disease

　　In recent years, a fungal disease called chytridiomycosis has been reducing or even wiping out frog populations in many areas around the world. Chytridiomycosis typically attacks the skin; a frog's skin is essential to many of its vital functions, including breathing and water intake. The fungus that causes chytridiomycosis has been found in the Sierra Nevada mountains, and it is quite possible that it is to blame for the decline of the yellow-legged mountain frog populations there.

　Third, not all frog species are vulnerable to catridiomycosis that fungal disease you read about. The skein of some frogs contains specific chemicals that protect the frogs against the fungus that causes the infection. Studies show that the skin of the yellow legged mountain frogs does produce protective chemicals of this type. So, since the yellow legged mountain frog seems capable of protecting itself from the fungus. It's not clear that it's the fungal disease that has brought down its population.

阅读

听力

　主题：保护mangrove trees

　　First, although some animals are known to damage mangroves, they can be controlled. Studies show that crabs, for example, like to feed on mangrove seedlings, eating most of the seeds produced by some species of mangroves. One proposal to combat this threat is to remove crabs from vulnerable mangrove areas and prevent them from returning by covering mangrove seedlings with a mesh, or web, that the crabs cannot penetrate.

　　First, crabs are not a serious problem for mangroves, and removing crabs is not a good idea. Crabs and mangroves have evolved together for millions of years. And they help each other in new ways. For instance. Perhaps indirectly provide mangroves with access to certain nutrients. You see, when searching for food, crabs, take deep holes in the ground near macro. The holes that the crabs make allow the underground rand grover's easier access to nutrients that managers. So despite causing some damage, products provide crucial benefits to mangos and should not be kept open for....

　　Second, governments have been successful in preventing destruction of mangroves by shrimp farmers. In one country where it is estimated that over half of the country's mangroves were destroyed in order to create new shrimp farms, farmers were required to shift to different methods of shrimp farming that do not involve cutting down mangroves. One such method utilizes wetland areas that are some distance away from mangroves, but are still suitable for raising shrimp.

　　Setting up shrimp farms some distance away from mangroves can still be quite harmful. Shrimp farms typically discharge a lot of waste water. This is polluted water that is a byproduct of a farming process and has to be removed from the. Typically, this wastewater is plumped into nearby rivers or streams. This dirty, polluted water sometimes flows into coastal areas where mangroves are growing. This can cause water quality in coastal areas to decline significant. Which is harmful for the entire ecosystem there, including ban. Thus, even trend farms in a distance doesn't really solve the problem.

　　Third, scientists have recently focused their efforts on techniques to help restore mangrove populations in areas that have sustained severe damage. An example of such techniques includes improving the quality of soil in areas that once had thriving mangrove populations that later became damaged or disappeared. Since soil quality impacts growth, improving soil quality will definitely help mangrove populations restore themselves.

　　Third, it's actually very difficult to achieve good soil quality in areas where manners once thrive but then disappear. You see, living mangroves have specialized roots that provide the soil with oxygen. The oxygen that mangrove is provide in turn allows the mangrove trees to thrive. But once mangroves die, the soil loses much of its oxygen. Once the oxygen is born, it's very difficult to replace it. And it's difficult for new mangrove trees to start brewing in such soil.

阅读

听力

　主题：guillemot海鸟的特点

　　Pattern

　　First of all, guillemot eggs come in many different colors, and each egg has a unique pattern of dark spots or speckles. Most birds produce eggs with a consistent appearance, so researchers have a hard time explaining why guillemot eggs are all so different. The unusual variety of colors and markings on guillemot eggs makes them interesting to look at, since each guillemot egg looks different from any other guillemot egg. But there seems to be no practical purpose for this unusual variation.

　　First, what's the purpose of the varied colors and speckling on the eggs? Well, guillemots live in huge colonies that include thousands of birds. You'll remember that guillemots lay their eggs on rocky surfaces. Sometimes an egg can roll a few feet away, and the guillemot needs to find it. But to do that, guillemot needs to recognize it. And that's exactly what the unique combination of color and speckling is for. It helps each guillemots distinguish its own egg from the eggs of all the other guillemots that live in the colony.

　　Surface

　　Second, the surfaces of guillemot eggs are oddly rough or bumpy in comparison with those of other birds' eggs. Researchers thought that this roughness might help guillemots keep the eggs balanced on top of their feet, which is how they usually hold the eggs. However, experiments and observations have not confirmed this hypothesis. The rough surface of guillemot eggs remains unexplained.

　　Second, researchers have also found out the function of the eggs from the surface. guillemots’ eggs naturally get covered in dirt. Dirt prevents the small bird growing inside the egg from breathing well. The rough surface helps as follows. When water gets on the egg, water from rainfall, for example, the rough surface makes the water form large, drops and roll down the egg. Large drops, clean dirt off the egg, very effectively. And so air can reach the chick inside more easily. By contrast, smooth eggs do not cause large water drops to form. If guillemots’eggs were smooth, water could not clean them very well.

　　Shape

　　Third, guillemot eggs are longer and more pointed than the eggs of almost any other bird species. For a long time, scientists believed that this shape prevented guillemot eggs from rolling all the way off the uneven rock surfaces and breaking on other rocks far below. However, it turns out that it is quite common for guillemot eggs to roll off rocks; the special shape does not seem to prevent this problem.

　　Third. The real reason for the shape the guillemots eggs, has to do with how guillemots protect their eggs from the cold ocean climate. The parents cover the eggs with their bodies but the Chick is growing inside. The long and pointed shape of the egg makes it fit very well with the shape in size of the parent's body. As a result, more of the egg's surface sees in contact with the parents’ body, and it's easier to keep the egg warm.