自考《英语（二）》试题练习：完成句子（11.29）
单选题
[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
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