15.We should prevent pollution-----happily.

15.We should prevent pollution_____happily.
A.from living B.to live
C.living D.to living
为什么是选B,不选A 呢
16.I’m examining the composition he has just
finished_____the possible mistakes in it.
A.to correct B.correct
C.corrected D.correcting
还有这题也是选A，为什么这种题都是选动词不定式，而不选动名词呢。