2025年8月27日上午场托福写作完整版答案及解析（含范文）

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　主题：Beaver dams

　　One of the benefits of beaver dams is that they increase the amount of water available to communities. Without dams, water would flow through rivers without stopping. Dams create a barrier in the river that slows the flow of water and keeps large quantities of it in the area. Not only do dams keep rivers full, they also allow water to seep down into the soil, penetrating land far away from the river bed. This increases the water supply for both townspeople and farmers, something which is especially important in times of drought.

　　First, beaver dams do increase local water supplies, but they sometimes also cause flooding. You see beavers often build dams in front of culverts. Culverts are special tunnels built beneath roads or railroads in places where the roads or railroads cross streams or small rivers. Culverts allow the flow of water to pass underneath the road. But when a beaver dam blocks a culvert. Water cannot flow through the tunnel and may flood the road above, damaging the roadway and even nearby houses.

　　Second, beaver dams significantly increase biodiversity (the variety of plants and animals) in the areas where they are located. Because dams help to store and retain water, there will be more vegetation, including grass, shrubs, and other plants alongside rivers with dams. Wildlife in turn are attracted by the vegetation, which provides food, shelter, and other benefits for a number of species, including birds, elk, and deer.

　　Second, beaver dams may increase overall biodiversity. But some types of organisms, especially trees, can be harmed by them in a couple of ways. Beavers harm some trees by chewing through their trunks and then using the wood to build dams. Once built, the dams themselves can harm even more trees because beaver dams cause water in rivers and streams to change course, slightly forming pools known as beaver ponds on previously dried land. These newly formed ponds can cover the roots of trees with water. And trees whose roots remain under water too long will die.

　　Finally, beaver dams can turn a river into an ideal habitat for certain types of fish. Since the water that accumulates behind a dam flows very slowly compared to water in other parts of the river, fish that prefer slow-moving water can inhabit rivers where there are beaver dams. This slow-moving water also provides a protective habitat for fish during the winter due to its relatively stable temperature.

　　Finally. It's true that beaver dams can benefit fish however this isn't always the case. One way beaver dams may harm fish is by creating a barrier that prevents fish from traveling forward. Dams usually have passageways between branches. However, fish can get stuck behind dams if the force of the water isn't strong enough to push them through. And because dams block water flow, they also increase the accumulation of sediment. Or dirt particles in the slow moving water behind the dam. Making the water dirty. Something that is especially harmful to young fish.

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　主题：theories to explain the phenomenon

　　One such explanation is that the stones are pushed by the wind. Scientists have recorded strong winds in the playa, and when it rains, the playa's muddy floor becomes slick and slippery. Under such conditions, powerful gusts of wind could give the stones a considerable push. The reduced friction of the muddy ground would then allow the stones to slide long distances. Adding to the strength of this theory is the observation that the stones often travel parallel to the direction of the most common prevailing winds.

　　First, it's true that the Racetrack Playa experiences powerful winds. But when the stones move, they leave rather deep grooves in the ground that dig into the valley floor. The grooves look like very deep tire tracks in the mud. This means the moving stones meet a lot of resistance. They're being pushed through the mud rather than just sliding or rolling on the surface. You would need a lot of force to push three hundred kilogram stones through the Playa muddy floor. And it is unlikely that even powerful winds have enough force to do that.

　　A second possible theory for the stones' movement involves ice formations. During the night, groundwater will occasionally seep up and form ice sheets on the ground. The ice sheets can trap stones within them. Ice sheets that form on sloping ground can start sliding slowly down the slope, pulled by gravity. Large and thick ice sheets would be able to drag along even heavy stones trapped within them. Over time the gradual sliding movement could transport the stones great distances.

　　OK, What about the ice sheet theory? Well, for this theory to work. Large and thick ice sheets would have to form. well, there may be some ice occasionally forming in the Racetrack Playa. But the conditions there are not really favorable for large scale ice formation. First, it's a desert area, so there's only a small volume of groundwater available. And the small amount of ground water is not the only limiting factor. The temperature may drop below, freezing at night, but then it rises during the day. So the temperature typically does not stay below freezing long enough to allow the ice sheets to grow and thicken to the size needed to trap and carry the stones.

　　A third explanation is that people move the stones as part of an elaborate joke. In recent years, there have been reports of other unusual phenomena like crop circles, which were at first hard to explain but later turned out to be the work of people playing jokes. It is possible that the sailing stones have been moved around by people rather than by any natural forces.

　　And third, although the sailing stones may seem like someone's idea of a perfect practical joke. There isn't any evidence that people move them. Researchers have never found human footprints or the footprints of a pack animal like a horse that could drag the stones. And since we can tell from the stones tracks that they sometimes move during muddy periods. It would be impossible for any individuals to move the stones without leaving some kind of tracks themselves.

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　主题：whether the first people to sail around Africa were Phoenicians

　　First, it's true that Phoenicians used rather simple sailing technology, but that doesn't mean the voyage was impossible. In fact, recently in the twentieth century, some scientists and shipbuilders built a copy of an old Phoenician ship to see how capable it was of sailing long distances. They used exactly the same materials and techniques that were available to Phoenician six hundred years BC. And guess what. The scientists successfully sailed this copy of an old ship around Africa, so Phoenician ships may have been good enough for a voyage like this.

　　First, it is highly unlikely that the Phoenician sailors possessed the necessary technology to sail around Africa as early as 600 B.C.E. The ships they built were small and held together only with crude wooden pegs. Also, the ships had only one simple square-shaped sail. While such technology might have been suitable to sail on the Mediterranean Sea near Phoenicia, it would not have been suitable for the long voyage in the open ocean around Africa.

　　Second, it's true that the ancient Egyptians were generally not interested in exploring areas outside Egypt, but Niko the second was a rather different kind of king in this respect. For example, he was very interested in water transportation and started major projects to connect Egyptian rivers and seas through canals. Nico probably wanted to explore the possibilities of water transportation in general for trading purposes. He could have hired the Phoenician sailors to sail around Africa to help him discover new trading partners.

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　　Second, it also goes against what we know about Egyptian rulers of the time to suggest that Necho Il ordered the expedition and hired the Phoenicians. Ancient Egyptians are understood to have been generally uninterested in exploring the world beyond their kingdom and the lands immediately surrounding it. Necho Il would have had no reason to hire Phoenician sailors.

　　Finally, the Phoenician sailors reported some facts that make it unlikely that they invented the story. They reported that when they sailed far to the south, they noticed that at midday, at twelve o'clock, the sun was in the northern part of the sky instead of the southern. Well, that's exactly what happens in the southern hemisphere. The sun appears in the northern part of the sky at midday, in contrast to what happens in the northern hemisphere, where the sailors were from. This information about the position of the sun would be hard to invent. The most likely explanation for it is that the Phoenicians had actually gone to the southern hemisphere and observed the sun themselves.

　　Third, it is possible that the account of a journey around Africa recorded in the ancient sources was just a story invented by sailors that later spread. It was not uncommon for people of the ancient world to make up stories and pass them off as truths, particularly when it had to do with the ocean. Stories of sea monsters and magical islands were also popular at the time, so in the same way, a story about a voyage around Africa could have been invented as well.