begindoing/to do

　　begin / start to do sth

　　begin / start doing sth.

　　1)　谈及一项长期活动或开始一种习惯时，使用doing.

　　How old were you when you first started playing the piano?

　　你几岁时开始弹钢琴?

　　2)　begin, start用进行时时，后面动词用不定式to do

　　I was beginning to get angry。

　　我开始生起气来。

　　3)　在attempt, intend, begin, start 后接know, understand, realize这类动词时，常用不定式to do。

　　I begin to understand the truth。

　　我开始明白真相。

　　4)　物作主语时

　　It began to melt.