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

24. To the couple’s comfort, their income is now double ______ it was five years ago£®

     A.that          B.than         C.which        D.what