英语的.It is very helpful to improve our English 请问这句话属于四大句型的哪种

形式主语 It
真正主语 to improve our English
系动词：is
表语：very helpful
句型：It is + adj.+of/for sb.to do sth.
e.g.It is very nice of you to help me.
It is necessary to study English hard.

It's+adj+to do
表示“做什么事怎么样”

it的用法，it 作形式主语也叫先行代词, to improve our English是真正的主语。实际意义为To improve our English is very helpful
同样的还有 It is necessary for us to learn something.
It is important to protect environment.
It is hard for us to distinguish what kind of sentences it belongs to.