Answer:

D

Explanation:

Heat transfer by convection occurs in gases, liquids, and solids. Convection is the transfer of heat through the movement of a fluid or gas. When fluids or gases are heated, their molecules move faster and become less dense, which causes them to rise. As the heated fluid or gas rises, it carries heat with it, and cooler, denser fluid or gas takes its place. This creates a circular motion known as a convection current, which transfers heat from one place to another. Therefore, option d is the correct answer.