noun或者adj.都可以.名词或者形容词,再高级一点,加从句也可以.

举几个例子：

It is a dog.

It is beautiful.

It is exactly what I want.这正是我所需要的.

另外It is .that.也可以表示强调句.

扩展资料

It is not clear what they want us to do.

我们不肯定他们要我们做什么。

It is quite possible that space and time are finite.

很有可能空间和时间是有限的。

It is important not to let things get out of perspective.

重要的是不要把事情轻重倒置。

It is difficult to find work in the present economic climate.

在目前这种经济大气候下很难找到工作。

It is less of a problem than I'd expected.

问题不像我预料的那么大。

It is important not to let production levels fall.

重要的是别让产量滑落。