一般时 to do to be done
进行时 to be doing
完成时 to have done to have been done
To speak good English is not easy.
or： It is not easy to speak good English.
(采用形式主语 it 以避免头重脚轻)
It took me an hour to do the work.
She decided to take the examination.
I hope to meet him soon.
They expected us to help them.
He wants his son to study hard.
不定式作宾补，如谓语动词是感官动词，使役性动词(see， hear， notice， watch， make， have， let...)，则不定式符号“to”须省略，但在被动语态中不能省。
I heard them sing in the classroom.
I made her clean the room.
The girl is heard to sing an English song.
To teach is to learn.
His job is to sell cars.
We come to school to study English.(目的)
= in order to
I hurried to the store， only to find it closed.(结果)
He asked for a piece of paper to write it on.
= to write it on the piece of paper.
The poor man has no house to live in.
= to live in the house.
Have you anything to do？
= to do anything
She seems to dance very well.(现在情况)
She seems to be dancing in the dancing hall.(正在进行)
She seems to have danced well.(过去情况)
Has was happy to have been staying with his uncle.(动作持续一段时间)