Direction: Read the following passages carefully and answer the question that follows.
Why doesn't the air remain still ? The reason is that air, when it becomes heated, becomes lighter, and it rises. When it rises, other air moves in to take its place. The temperature of air becomes like the surface of the earth over which it travels. Over dry land, the air can become very hot. Then, when the sun goes down, it cools off quickly. Over the water air heats up more slowly and cools off more slowly. These changes cause the movement of air,which we call wind.