to做介词的时候就接名词，动名词，或者名词性结构，构成不定式时，就接原形。
例句
She will have to go to school.
她将不得不去上学。
It pleased him to talk to her.
和她谈话让他高兴。
I managed to swim to safety.
我设法游到安全处。
I had to go to the hospital.
我得去医院看病。
He loved her to sing to him.
他喜欢让她唱歌给他听。
She refused to submit to threats.
她面对威胁，拒不低头。
