第1个回答 2011-09-03
it通常是代词,常用作形式主语
is 是系动词
it is的句型常见的有这几种
1 it is +形容词/名词+for sb to do sth.
eg, it is hard for you to finish it alone
it is your duty to look after your old parents.
2 it is +形容词(人的性格等)+ of sb to do sth.
eg, it is kind of you to help me.
3 强调句型 it is +被强调部分+that+其他
eg, it is you that are to blame.