Which Number on This Figure Indicates Transfer of Thermal Energy

Multiple Choice

Which number on this figure indicates transfer of thermal energy by a convection cell?

A) 1, direct contact between the burner and the pan
B) 2, heating by thermal radiation through the air
C) 3, heated water expands and rises to the top of the pan and then cools and flows back down
D) 4, moving a pan of water away from the stove