8.11 begin(start) doing/to do
?
 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.