16.___________________　　　　 17.___________________　　　 18.______________

　 19.___________________　　　　 20.___________________

35. Special attention should be paid ______ our earth from __________ .

A. to prevent ; being polluted　　　　　　　 　　　 B. to prevent ; polluting

C. to preventing ; being polluted　　　　　　 　　　 D. to preventing ; polluted