A. argue

B. to argue

C. arguing

D. being arguing

17.Nowhere in nature is aluminum found free, owing to its always ___with other elements, most commonly with oxygen.

A. combined

B. having combined

C. combine

D. being combined

18.They stopped ___, but now I’m getting interested.

A. listening

B. to listen

C. listen

D. having listening

19.I am sorry to hear that you resorted ___

A. to cheat

B. to cheating

C. cheating

D. cheat

20.He wasn’t asked to take on the chairmanship of the society, ___ insufficiently popular with all members.

A. being considered

B. considering.

C. to be considered

D. having considered

答案：1-5 ADDCD 6-10 ACCAC 11-15 CCDCA 16-20 CDBBA