how do you do?和nice to meet you.在用法上有什么区别?什么情况下用?

问题描述:

how do you do?和nice to meet you.在用法上有什么区别?什么情况下用?
还有,it和that作代词有什么区别?怎么用?
that不能作主语吗?is that so?

看场合,反正觉得现在how do you do用得很少了
nice to meet you初次认识也可以用,比较正式
nice to see you就一般用在认识的人了