|8.11 begin(start) doing/to do|
begin / start to do sth
begin / start doing sth.
How old were you when you first started playing the piano?
2) begin, start用进行时时，后面动词用不定式to do
I was beginning to get angry。
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。
It began to melt.