— Why did the dinner party start so late last night?— It was _____ that caused him to serve dinner an hour later than usual. 

It ___ the students in your class who came to see you then.

It was the hurricane ________ was called Sandy ________ left at least 10 people dead and hundreds of thousands without power on the eastern coast of America. 

It_____we had stayed together for several weeks_____ I found we had a lot in common.

I wonder        that makes him so sad.