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

考查被動語態。此處harm是不可數名詞，用單數。句意：一旦對環境造成傷害，它需要花費多年的時間回復生態系統。