know
1.know作“认识（某人）”解，know of作“知道有（某人）”解。例如：I know of him, but do not know him (personally). 说“知道有…”必须用of。例如：Do you know of any such shop in your city? 但know the fact和know of the fact都可以说。
2.I am glad to learn that...等句子里通常用learn，不用know。
3.Who do you think he is? 等句子里该用think，不可用know。
4.have known后面接宾语和不定式的时候，那不定式可以有to，也可以没有to。例如：I have known him (to) say this before. never knew和have never known后面接宾语和不定式的时候，那不定式没有to，如I never knew him say this before和I have never known him say this before。假使have known，never knew或have never known改成被动语态，那不定式必须有to。例如：He has been known to say this before. He was never known to say this before. 和He has never been known to say this before.
假使have known，never knew或have never known的宾语后面的不定式是be，必须有to。例如：I have known him to be too busy to study. I never knew him to be too busy to study. 和I have never known him to be too busy to study.
5.注意下面第一句里用I know it，第二句里用I know：
- He is going to get married, and I know it.
- When his sister said that he was going to get married, I said, 'Yes, I know.'
