once harm____(do)to the environment,it takes years to have the system recovered.

2025-05-30 04:09:43
推荐回答(3个)
回答1:

done,完成时,表示"一旦破坏了环境"

回答2:

did,虚拟语气

回答3:

is done

once harm IS DONE to the environment,it takes years to have the system recovered.