A、By reducing the growth of weeds. B、By letting animal waste do the job of natural fertilizer. C、By keeping grasslands in good c

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. (16)Rotational grazing can even help prevent wildfires by keeping grasslands in good condition. (17) 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. (18)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. (18)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.
16. How can rotational grazing help prevent wildfires?
17. What will happen if animals stay in one place and eat what they like?
18. What are needed for rotational grazing?