21. It is human beings who should be responsible _______ the harm done to nature£®

A.to                B.for                C.with          D.of

22. Their plan was ______. With it we had little trouble in finishing the work.

   A.success       B.succeed      C.a success      D.a successful

23. Important people don’t have much free time as their work _______ all their time.

A. takes away     B. takes over     C. takes up      D. takes in