1) 談及一項(xiàng)長(zhǎng)期活動(dòng)或開(kāi)始一種習(xí)慣時(shí)，使用doing.
How old were you when you first started playing the piano?
你幾歲時(shí)開(kāi)始彈鋼琴?
2) begin, start用進(jìn)行時(shí)時(shí)，后面動(dòng)詞用不定式to do
I was beginning to get angry。
我開(kāi)始生起氣來(lái)。
3) 在attempt, intend, begin, start 后接know, understand, realize這類動(dòng)詞時(shí)，常用不定式to do。
I begin to understand the truth。
我開(kāi)始明白真相。
4) 物作主語(yǔ)時(shí)
It began to melt.
