begin / start to do sth

begin / start doing sth.

1)談及一項長期活動或開始一種習慣時，使用doing.

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

你幾歲時開始彈鋼琴?

2)begin, start用進行時時，后面動詞用不定式to do

I was beginning to get angry。

我開始生起氣來。

3)在attempt, intend, begin, start 后接know, understand, realize這類動詞時，常用不定式to do。

I begin to understand the truth。

我開始明白真相。

4)物作主語時

It began to melt.