Man: I think its going to snow. Woman: Going to snow？ The ground is already covered! Quest

In "I think it impossible for man to live on the Mars", "it" is the ______ of the sentence

【D1】SPEAKER A: ARE YOU GOING TO THE PARTY ON SATURDAY？ SPEAKER B: I WAS THINKING ABOUT IT

【D2】SPEAKER A: ARE YOU GOING TO THE PARTY ON SATURDAY？ SPEAKER B: I WAS THINKING ABOUT IT

【D3】SPEAKER A: ARE YOU GOING TO THE PARTY ON SATURDAY？ SPEAKER B: I WAS THINKING ABOUT IT

I think I should prefer to go on Thursday,______ it s all the same to you.A．as ifB．ifC．unl

I think it unnecessary to go back there, _____we have visited these places.Aso thatBin