【正确答案】topic In the lecture, the professor refers to two methods to deal with soil erosion on mountain sides. example 1 The first method is to grow various crops, plant the crops with other types that have deep and strong roots. On the one hand, these crops can hold the soil firmly by themselves; on the other hand, as a result of the different mature time among the crops, when the farmers harvest one type, the other types are still in the ground, holding the soil tightly. example 2 The second method is to reduce rain flood by building channels. When the rain falls, the channel can direct rain flood water away from the lower land. Although the plants in the area will get wet, the soil will escape from being swept away because of the channels.

【答案解析】[听力原文] W: Farming in some locations like mountain sides is usually faced with various challenges due to certain types of terrain. Soil erosion is one of them. Precious nitrogen and fertile soil which crops need to grow with can be easily swept away by naturally occurring rainfalls in the area. But what can we do to fight soil erosion? Well, two possible methods can prevent soil from being eroded, which I am going to explain to you. The first method is simply to grow a diversity of crops. Plant crops along with other types of crops which have deep strong roots that can hold the soil firmly. Also, the different crops will not mature at the same time, which means while the farmer has harvested one type, the others will still be in the ground holding the soil in place, therefore keeping the crop fields and soil from being mobile. The second method is to reduce the rain flooding to the surface of the soil. By building channels for rain water to flow off the field, the erosion effect is lessened. When it rains, the water flows into a channel and is directed away from the lower parts of the field. The crops will still get wet from the rain, but the rain flood water will do no harm to the crops land due to the channels.