单选题 Questions 16 to 18 are based on the passage you have just heard.
【正确答案】 C
【答案解析】[听力原文]
Grasslands need time to rest when cattle and other animals feed on them. Moving animals from one area of pasture to another can provide the time needed for new growth. This is called rotational grazing. Experts say rotational grazing is good for the land and the animals, and it can save money. This form of grazing can reduce the need for pesticide treatments by reducing the growth of weeds. And it can limit the need for chemical fertilizers by letting animal droppings do the job of natural fertilizer. Rotational grazing can even help prevent wildfires by keeping grasslands in good condition . Letting animals feed continually and intensively in the same grazing areas can require costly replanting. Animals eat the most desirable growth first. When that keeps happening, the roots do not have enough time to recover. As a result, less desirable plants may replace them. Intensively used grasslands are also harmed as the soil is continually crushed under the weight of heavy animals. And the animals usually avoid their own waste, which reduces the amount of good grazing space even more. Experts say that while rotational grazing can save money over time, it also requires planning . And that starts with a good map to mark fences, water supplies and grazing areas. Changing methods of grazing also requires time . Farmers may want to put up electric fences to enclose grazing areas, called paddocks (小牧场). The paddocks will need water. Some farmers design paths for animals from different paddocks to drink from a common watering place.

How can rotational grazing help prevent wildfires?

[解析] 短文中提到,循环放牧还可以使草地状况保护良好,以此来防止野火的发生。
【正确答案】 C
【答案解析】[听力原文]
What will happen if animals stay in one place and eat what they like?

[解析] 短文中提到,如果动物在同一个地方连续不断地集中吃草,就要重新种植牧草,成本比较高。动物会首先食用长势最好的牧草,如果这种情况吃寻发生牧草根部没有足够的时间来恢复。最终,长势稍差的牧草会取代长势较好的牧草。
【正确答案】 C
【答案解析】[听力原文]
What are needed for rotational grazing?

[解析] 短文中提到,专家们认为循环放牧从长远来看会节省资金,但它页需要计划;下文中又提到,更改放牧方法也需要时间。综合理解可知,循环放牧需要的是计划和时间。