The reason for his success is ______ he worked very hard.

________ time went by, small clever animals covered the earth and have become the most important animals on the planet.

. It is only when we cannot see clearly _____ we come to see ______ important our eyes are.

The house, ______walls are red, is where my grandfather used to live ten years ago.

—What are you going to do this afternoon?—I’ll probably go for a walk later on________it stays fine.