【托福写作机经】2025年7月19日下午场托福考试回忆

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　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.

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　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.

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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