单选题
[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
答案解析：本段文字讲的是：受到工业污染的土壤含有重金属，而重金属很稳定不容易降解，其中的某些微量重金属能使人致癌或中毒。可以看出其中心内容是：受污染土地的潜在危险，选择B。