Relative clauses

Hi everyone.

In a textbook, I found the following:

* The hotel has a swimming pool. It is very big. (Combine with a relative clause)

The answer is: The hotel has a swimming pool that is very big.

Question 1: Why is there one answer? why can't we say it like this:

"The hotel that is big has a swimming pool ."?

Question 2: Is it true that the clause is defining(restrictive) because there is an indefinite article before the noun' a swimming pool'?

Or can we say that the pronoun "it" should refer to the part " the pool" not to the whole" the hotel"?