It was in the small house    was built with stones by his father  he spent his childhood. 

I just wonder _____ that makes him so excited?

It was my sister        first had the idea to cycle along the river. 

—Why is it ________ so many people enjoy eating on the run?—Of course, the most obvious answer is that fast food is fast.

It was when Asimov was eleven years old ________ his talent ________ writing became obvious.