是ask for leave 还是ask for leaving,为什么在介词后可以直接加动词原形,还是此出不是动词?

是ask for leave 还是ask for leaving,为什么在介词后可以直接加动词原形,还是此出不是动词? ask for leave还是ask for a leave还是ask for leaving ask sb.for help中的help是名词还是动词? ask for leave 还是 ask for a leave? ask for a leave 还是ask for leave “You can go and ask Peter for help”为什么结尾不是"helping"?不是介词后的动词 leave for 到底是动词短语还是介词短语? need不是非及物动词吗?为什么可以在needn't后直接加动词原形? ask sb.后跟动词不定式还是跟动词原形 All you need to do is ask the question 为什么 is 后可直接加动词原形 understand后加to 动词原形还是动词过去式,还是直接加动词ing. 为什么是ask for “for”是什么意思,为什么不是ask to