What is formed when hot material rises and cool material sinks in convection?

Correct answer: Convection cycle

The direct answer is option A: the rising and sinking of hot and cool material forms a convection cycle. Heating usually makes material less dense, so it rises. Higher material cools, becomes relatively denser, and sinks. This continuous movement creates a circulating cycle called convection. Option A is correct because it names the process produced by both upward and downward movement. Option B, a river delta, forms where a river deposits sediment near its mouth; it is not created by mantle convection. Option C, a desert dune, forms mainly through wind-blown sand. Option D, a glacial lake, forms through glacial erosion or melting ice. Thus the fact chain is heat difference, density difference, rising, cooling, sinking, and circulation. Memory cue: hot rises, cool sinks, and the loop is convection.