It hot, we went for swimming.（误）
It being hot, we went for swimming.（正）
it being 独立主格结构例句
It being a raining day, we gave up our plan to go hiking.
It being a Sunday, we had the day off.
It being Christmas,the government offices were closed.
It being a holiday,all the shops were shut.
It being Sunday, we went to church.
It being Sunday, all the offices are closed.
It being Naional Day today,the streets are very crowded.（=As it is National Day today,the streets are very crowded.）
It being late, they insisted on leaving right now.