【托福写作机经】2025年3月1日托福考试回忆【下午场】

阅读

听力

　　 主题：关于植物knees功能的假说

Oxygen absorption

First, knees may help the trees' roots absorb or take in oxygen. Plant roots require oxygen for important cellular functions, and the soil in the watery habitats where cypress trees often grow is low in oxygen. Roots of plants growing in low-oxygen soil must often obtain oxygen from another source. For example, mangrove trees, which also grow in soil that is underwater, are known for having above-ground roots that absorb oxygen. Like the roots of mangroves, cypress knees may take in oxygen from the air and deliver it to the deeper roots.

First, it seems reasonable that a structure sticking up into the air would help absorb or take in oxygen. But researchers tested this hypothesis. They place cypress knees in tightly closed containers with oxygen. And measured how the oxygen levels inside the container changed over time. Surprisingly, they found that the oxygen levels did not change much. This indicated that the knees absorbed very little oxygen. If the function of cypress knees were to take in oxygen, you would expect the knees to absorb significant amounts of the oxygen in the containers. That did not happen.

Additional stability

Second, knees may help cypress trees stand firmly in the soil, making them better able to remain securely in place when exposed to high winds or strong water currents. The fact that the cypress has knees in addition to a network of roots may provide additional stability, allowing the tree to anchor itself well in the soil. Cypress trees may need this additional support due to the softness of the wet soil in which they grow.

Second, the idea that knees help cypress trees stay firmly rooted in the soil is problematic, too. You see. Many cypress knees are attached to the cypress's horizontal roots. Those horizontal roots do not extend down deep into the soil. And the knee does not provide any additional stability in that situation. These can help with stability only if they're attached to vertical roots that reach deep into the soil. But many knees are not connected to vertical roots at all. Since the knees are so frequently attached to horizontal roots rather than to vertical ones, it's doubtful that physical support is their main purpose.

Methane release

Finally, knees grow on trees in areas where methane gas exists in the soil. The knees are in direct contact with the soil infused with methane, which is of no use to trees. Therefore, the function of knees may be to release methane gas from the trees' roots into the air. The fact that measurable amounts of methane have been detected in the air above the knees supports this idea.

Finally, about methane release. This idea is unconvincing for a couple of reasons. You see, although methane is not useful to trees, it really does them no harm. It seems unlikely that the trees would develop special features like the knees just to get rid of something that has no negative effect. Besides, lots of microorganisms live on cypress knees. And it's completely possible that these tiny organisms produce the methane detected around the knees. Not the knees themselves.

阅读

听力

　　 主题：金星上灰光的来源

1.闪电活动(Lightning activity)：金星上的灰光可能是由频繁的闪电活动产生的。金星的大气层中含有大量的云层和带电粒子，这些云层在运动过程中会产生强烈的摩擦和碰撞，从而引发闪电。闪电释放出的光亮在金星的夜半球就可能表现为灰光，就像地球上的闪电在特定条件下也会产生明显的光亮一样。

1.目前的观测技术已经能够较为准确地探测到金星上的闪电信号，但实际探测到的闪电频率和强度远远不足以产生我们所看到的灰光。也就是说，即使金星上存在闪电活动，其产生的光亮也太微弱，无法解释持续且明显的灰光现象，所以闪电活动不太可能是灰光的主要来源。

2.磷化氢化学反应(Chemical reaction of phosphine)：金星大气层中存在磷化氢(Phosphine)，它可能与其他化学物质发生化学反应，进而产生发光现象。磷化氢是一种具有特殊化学性质的物质，在金星的大气环境中，可能与氧气、二氧化碳等发生反应，反应过程中释放出能量并以光的形式表现出来，形成我们所观测到的灰光。

2.虽然金星大气层中存在磷化氢，但根据现有的化学模型和实验，磷化氢与金星大气中其他物质发生反应所产生的能量和光亮非常有限，难以达到灰光所呈现出的亮度和持续性。因此，磷化氢的化学反应不太可能是导致灰光出现的原因。

3.太阳反射(Sun reflection)：金星的某些表面特征可能会反射太阳光，从而形成灰光。金星表面有山脉、峡谷等不同的地形，这些地形在特定的角度和光照条件下，可能会像镜子一样反射太阳的光线。当这些反射光在金星的夜半球被观测到时，就可能呈现为灰光。

3.金星的自转速度非常缓慢，而且其表面的地形和物质分布使得太阳反射光很难在金星的夜半球形成稳定且明显的灰光。从理论上来说，太阳反射光在经过金星大气的散射和吸收后，到达夜半球时的强度已经非常微弱，无法形成我们所观测到的较为显著的灰光现象，所以太阳反射也不太可能是灰光的来源。

阅读

听力

　　 主题：动物为什么玩耍

The first theory is called the surplus energy theory. This theory maintains that some animals, mammals for example, are so efficient at using energy that they often do not manage to spend all the energy they receive through food. They end up with unused, surplus energy that they cannot store. According to this theory, animals have to play to get rid of the surplus energy that they have not used.

Let's take the first theory, the surplus energy theory. This theory is contradicted by observations of marine mammals such as seals. Young seals sometimes have to survive alone for days, waiting for their mothers to bring food from far away. During that time, the young seals have no energy intake. As the days pass, they have very little stored up energy remaining, certainly no surplus energy. and yet. They still play, even though they have no energy to spare.

A second theory is called the instinct-practice theory. It states that young animals play as part of their physical education. The physical actions that animals will need to use for survival are instinctual, that is, preprogrammed in their brains. The animals, however, have to train their bodies to be able to perform these actions. So this theory explains why the play of young animals centers on real-life tasks. For example, predatory animals—those that hunt, kill, and consume other animals for food—have often been observed attacking and biting during play, which are precisely the skills they will need in order to hunt for food.

Now about the second theory, the instinct practice theory, the problem is that in some animals, playing and practicing don't seem to make much difference when it comes to hunting skills. In one experiment with cats, for example, researchers permitted one group of young cats to play, but they did not allow cats and another group to play. The researchers thought that the cats that were permitted to play would become better hunters. That didn't happen as the animals grew older, the cats that had played were not more skilled in hunting than the other cats。

A third theory, called the social functions theory, is that animals play to establish social relationships within their group. Basically, play gives animals a chance to bond with the other members in their group. For example, in a study of rats, those that played together made high-pitched squeaks that were accompanied by the release of pleasure-causing chemicals in the brain. This association of play with pleasure may motivate the animals to stay together as a harmonious group even while not playing.

And how about the third theory? The social functions theory. Well, although playing may help rats socialize with one another. Play is probably not necessary for rats to develop social behavior. Rats only play when they're very young. But scientists observe that the region of a rat's brain that's important for social behavior can develop even when rats are older and don't play anymore. In other words, rats can develop the ability for social behavior even after they've passed the age when they play.

阅读

听力

　　 主题：犀牛转移能否有效保护犀牛

1.犀牛在relocation的过程中有2%-5%的死亡率。众所周知，犀牛是濒危物种，因此在运输过程中造成犀牛死亡，这中做法是不可取的。

1.虽然犀牛在运输途中不可避免地会发生伤亡，但是死亡的犀牛毕竟是少数。特别是把运输途中犀牛死亡率和盗猎者猎杀犀牛导致的死亡率对比时，会发现运输途中犀牛死亡数量远远低于盗猎者猎杀犀牛的数量。相比两种情况，还是relocation更好一些。

2.犀牛有着非常紧密的种族社会关系，如果把犀牛relocate的话，就会造成公犀牛和母犀牛的数量不平衡，会对犀牛的繁殖造成影响，此外它们的种族纽带也会被切断。

2.阅读中所提到的犀牛性别不平衡问题在进行relocation之前就可以避免。保护者们会挑选一定数量的公犀牛和母犀牛，保持比例平衡。另外带着幼崽的母犀牛不会进行relocation，不会拆散它们的社会关系。

3.relocation不能完全防止偷猎者猎杀犀牛，因为犀牛角的价值很高，所以就算把犀牛运到别的地方偷猎者还是会紧随不放，所以不能从根本上解决问题。

3.把犀牛运到别的地方，那里地域广阔，犀牛有很大的活动空间，盗猎者在如此大的范围之内发现犀牛非常困难。另外，有些地方人很难通过，偷猎者无法到达。

阅读

听力

　　 主题：把二氧化碳储存在地下

Storage

First, there is the question of whether locations proposed for storing CO2 have enough space. The burning of fossil fuels around the world releases billions of tons of CO2 into the atmosphere annually. In order to make & considerable difference in combating global warming, most of the released CO2 would need to be captured and stored underground. It is not clear whether underground sites suitable for CO2 storage have enough space.

First storage. Well, carbon dioxide doesn't gas under normal conditions. Gases definitely take lots of space. But if the CO2 is exposed to high pressures and the high temperatures before being stored underground, it will transform from a gas into a super critical fluid. Super critical foods are more compressed and therefore occupy less space than gases. If we process CO2 at high pressures and temperatures and then store it as a super critical fluid, it will take up less space. Which decreases the need for so much storage space.

Health Risks

Second, if CO2 escapes from underground storage sites, it can pose risks to human health. CO2 leaks may occur if, for example, unforeseen natural processes or forces create cracks in the ground above the storage site. Although the normal atmospheric levels of CO2 are harmless, high concentrations of CO2 may be unsafe, causing headaches, tiredness, and possibly even death.

Second, we can minimize the health risks in CO2 weeks based on research that has been done on them. Carbon dioxide leaking from the underground storage units usually stays close to the ground. This means that people would only get sick if they breathe the air close to the ground. For example is they were sleeping on the ground while camping. So we can take appropriate safety measures. We can install monitoring devices in areas where CO2 is stored. When the monitoring devices detect CO2 they will sound a warning to alert people to leave the area quickly and not breathe the air close to the ground.

High Costs

Finally, a wide range of costs are associated with the process of storing CO2 underground. First, new technologies for capturing and storing CO2 that currently do not exist will have to be created. In addition, new infrastructure, such as pipelines transporting CO2 from industrial facilities to storage sites, will have to be built. All of these requirements will likely result in very high costs for constructing and operating CO2 storage systems.

Finally, some of the costs can actually be offset by financial benefits. For example, some of the sites suitable for CO2 storage are deep underground layers of rock that contain another gas called methane. When carbon that is injected into those rocks, the rocks release the methane gas. Methane is commercially valuable as fuel, and so the methane released at the storage sites can be collected and sold. Profits from selling methane can at least partly make up for the high costs of carbon dioxide storage.