三题答案该如何选,英语高手请进1.When he got off the bus,it happende_____.A.

三题答案该如何选,英语高手请进
1.When he got off the bus,it happende_____.
A.to rain B.to be rainging C.raining D.to raining
为什么选B而不A或是C
2.The bird was lucky that it just missed______.
A.catching B.to be caught C.being caught D.to catch
为什么C而不选A
3.It was polite for the young ____theri seats to the old.
A.giving up B.to give up C.being given up D.to be given up
为什么选B而不选C
我个人感觉自己可能是关于动词不定式与动名词的用法有点搞晕了,上面三题有点没太弄明白,希望高手能给一些指导,