The day being hot

[joham]

_______, we went swimming in the sea.

A. The day being very hot B. It being a very hot day
C. The day was very hot D. Being a very hot day


The given answer is B. I should think A is fine too. Am I right?

Thank you in advance.

 

[5jj]

_______, we went swimming in the sea.

A. The day being very hot .. B. It being a very hot day ..C. The day was very hot .. D. Being a very hot day

The given answer is B. I should think A is fine too. Am I right?

Yes, you are correct.
You will also hear many people saying D, though it is grammatically incorrect. Do not use D in an examination!