Question

Once harm ______ to the environment, it takes years to have the system recovered.

A. does　　　　　 B. is done　 C. will be done 　　 D. be done

 

Answer 1

B

 

考查被动语态。此处harm是不可数名词，用单数。句意：一旦对环境造成伤害，它需要花费多年的时间回复生态系统。