begin / start to do sth
　begin / start doing sth.

1)　談及一項長期活動或開始一種習(xí)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(jìn)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.