He does exercise _____ keep fit用什么介词

问题描述:

He does exercise _____ keep fit用什么介词

应该填to.
不过to在这儿不是介词,是动词不定式的标志,to keep fit作目的状语.
整句话意思:他运动是为了保持健康.为什么不用for如果填for,后面应该说成for keeping fit(因为for是介词,后面不能跟上动词原形,要用doing) 另外,如果表示目的,for后面只能加上名词,不能跟上doing,如:He came here for the tickets.(比较:He came here to buy the tickets.)除非在固定搭配中用for的后面可以跟上for doing,如:Tom was praised for cleaning the room after the party was over.(在这个句子中不能说Tom was praised to clean the room ...)