单选题
1.【完成句子】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.
Industrially contaminated sites usually require a thorough clean-up due to __________.
A.the persistence of heavy metals
B.industrially polluted soils
C.naturally polluted soils
D.rock and soil chemistry
正确答案:A
答案解析:本段提到:受到污染的土壤含有重金属,而且重金属很稳定,不容易降解,所以要对重金属进行彻底的清除。答案选择A。