【概括大意】Heavy metals are persistent; they do not break down to other chemicals in the environment. Industrially polluted sites usually undergo intensive clean-up and rehabilitation because heavy metals are a health concern once they enter the food chain. Some trace metals are alleged to cause cancer and are also known to cause poisoning.
The main idea of this paragraph is__________.
A.The Nature of Heavy Metals B.Potential Hazards of Human Contaminated Soils C.Heavy Metals and Food Chain D.Research on Channels of Heavy Metals Getting into Human Food Chain正确答案B
