Correct option is B. Convection
(a) Conduction is the process of transmission of heat in a body from the hotter part to the colder part without any bodily movement of constituent atoms or molecules of the body.
(b) In convection, the heated lighter particles move upwards and colder heavier particles move downwards to their place. This depends on weight and hence, on gravity.
(c) Radiation is the process of transmission of heat from the body to another body through electromagnetic waves through vacuum, irrespective of their temperatures.
Hence, (b) is correct.