【单选题】听力原文: Scientists have discovered that plants themselves pro-duce many poisonous chemicals for defense against insects. But insects have developed ways of dealing with them and, in fact, have been eati...
A.
Insects have developed some sort of resistance to man-made poisons.
B.
Insects have been eating plants for about 250 million years.
C.
Farmers sometimes use a combination of two or three insecticides at once.
D.
New insects mate with insects which survived from a certain kind of insecticide.