选择合适的句子,补全对话。

A. How do we use water? B. What should we do? C. Where does water come from? D. When do we need water? E. Does water come from the rain, too?

John: Water is very important. 

Mary: It comes from the sea.

John:

Mary: Yes, you are right.

John:

Mary: We use water to wash clothes.

John:

Mary: When we are thirsty.

John: Water is so useful.

Mary: We should keep the water clean.