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.
It is my pen that provides me more chances to win the game正是我的这把钢笔,给我提供了更多机会赢得比赛.