摘要
<正>1. It’s time for sb. to do sth.是某人做某事的时候了2. It takes sb. some time to do sth.花费某人多少时间做某事it是形式主语,真正的主语是动词不定式to do sth.。3. keep(on)doing sth.一直坚持做某事keep doing sth.一般用于静态动词。keep on doing sth.意为"继续不停地做某事",一般用于动态动词,但二者的区别并不是很严格,有时可以互换。4. keep...from doing sth.阻止,(使)免于做某事