While it is raining- Clause

I was studying about clauses in a book and then a sentence came which seemed pretty abstruse to me.

The book says that in the sentence: "We can't start while it is raining," the "while it is raining" part forms a clause.

Can anybody please tell me what the subject of this clause is? Is it 'it' or 'while'. Kindly provide explanation too so that I can understand it well.

Answer

When the book says 'while it is raining' is a clause, it actually means 'it is raining' is a clause, without 'while'.

We can't start while it is raining.

Means:

We can't start during the time it is raining.

Just as you can't say 'during the time it is raining' is a clause, neither can you say 'while it is raining' is a clause.