A hot sun warms the surface of a lake on a calm day. What will happen to the cold water at the bottom of the lake?
A. The cold water at the bottom will rise up and mix with the warm water at the top.
B. The warm water at the top will sink down and mix with the cold water at the bottom.
C. The cold water will remain at the bottom and will not mix with the warm water at the top.
D. Both A and B are true.