1)enough answers (adj.enough questions是复数,所以,answer也要加s)
2)meeting different (like doing)
3)happily happy (look at固定搭配,happily修饰动词 而look单独用时是系动词,后面直接加形容词)
4)a difficult problem (这个、应该没什么理由吧)
5)B (begin to do/doing 还没做,用前者;做了的,用后者)
6)a clever/smart child (同4)