What role does heat play in the formation of convection currents

Heat causes expansion as it raises the temperature of the individual molecules of the substance, thereby causing the kinetic energy of individual molecules to rise and vibrate relative to one another

Explanation:

As heat is applied heated fluid expands, hence become less dense. The less dense heated fluid rises away from the heat source. As it rises, it pulls cooler fluid down to replace it. This fluid in turn is heated, rises and pulls down more cool fluid. This upward and downward movement of fluid due to density gradients is call convection current

real, smaller and upside-down.   so the answer should be b.