Nearly all our food comes from the soil. Some of us eat meat, of course, but animals live on plants. If there were no plants, we would have no animals and no meat. So the soil is very necessary for life. The top of the ground is usually covered with grass or other plants. There may be dead leaves and dead plants on the grass. The waste matter   from animals also falls on it. All soil needs food. If we do not give it any, the plants will be weak. Farmers found that animals' waste is the best food for the soil, but chemical fertilizers   are also very useful. The same crop   should not be grown in the same place every year; it's better to have a different crop. A change of crop and the use of a good fertilizer will keep the land good. Why do we often grow a different crop in the same place every year?
Because we can keep the soil rich this way. Because we don't have enough land. Because we want to have a different food. Because we do this as a habit.
Question: Nearly all our food comes from the soil. Some of us eat meat, of course, but animals live on plants. If there were no plants, we would have no animals and no meat. So the soil is very necessary for life. The top of the ground is usually covered with grass or other plants. There may be dead leaves and dead plants on the grass. The waste matter   from animals also falls on it. All soil needs food. If we do not give it any, the plants will be weak. Farmers found that animals' waste is the best food for the soil, but chemical fertilizers   are also very useful. The same crop   should not be grown in the same place every year; it's better to have a different crop. A change of crop and the use of a good fertilizer will keep the land good. Why do we often grow a different crop in the same place every year?
A. Because we can keep the soil rich this way.
B. Because we don't have enough land.
C. Because we want to have a different food.
D. Because we do this as a habit.
Answer: