一道非谓语选择1．---What's the matter?---I smell something ＿＿．A.burn

一道非谓语选择
1．---What's the matter?
---I smell something ＿＿．
A.burn B.burns C.being burnt D.burning
注：答案是选D,为什么不能选C呢?
2．Upon hatching,_____ .
A.young ducks know how to swim
B.swimming is known by young ducks.
C.the knowledge of swimming is gained by young ducks
D.how ti swim is known in your dicks
注：hatch表示孵出,应该是被孵出吧,可为什么是主动呢．
非谓语中哪些词是主动表被动的?