英语句子中,在什么后面动词是原形的?

TO
DO/DON'T
DOES/DOESN'T
LET
CAN

TO作动词不定式时,作介词时跟ING形式当然还有情态动词后

1．to作动词不定式时
2．情态动词后是动词原形
例如can(could),may(might),be able to,must,have to,need,dare,will(would),should,ought to,had better,would rather
等

help (do ) sth.

助动词(do does)，情态动词(must can)，不定式(to),使意动词（let make),或在固定搭配中

动词不定式to
情态动词must do/did/does must can may等