1) 谈及一项长期活动或开始一种习惯时,使用doing.例如: How old were you when you first started playing the piano?你几岁时开始弹钢琴? 2) start用进行时时,后面动词用不定式to do.例如: I was starting to get angry.我开始生起气来. 3) start 后接know,understand,realize这类动词时,常用不定式to do.例如: I start to understand the truth.我开始明白真相. 4) 事物作主语时.例如: The snow start to melt.雪开始融化了