must not 后面加do doing 还是to do?

must not 后面加do doing 还是to do? Why not 后面+doing 还是to do? "why not "后面加do还是to do还是doing?为什么?能不能具体点? hard后面加doing还是to do refuse后面加to do 还是doing discover后面加to do还是doing? adjust to 后面加doing还是do? spend后面加doing还是to do? ask后面是加to do还是doing,还是do? dislike后面加to do还是do 还是doing why not后加do还是doing还是to do? must 后面是加to do sth.还是do sth.