Explanation:

Heat transfer is the process of thermal energy moving from one object or substance to another. There are three main methods of heat transfer: conduction, convection, and radiation. Gravity plays a role in convection but not in radiation and conduction.

Conduction:
Conduction is the transfer of heat through direct contact between particles. In this process, heat energy is transferred from the particles with higher kinetic energy (hotter particles) to the particles with lower kinetic energy (cooler particles). Gravity does not play a part in conduction as it is solely dependent on the interaction between particles.

Convection:
Convection is the transfer of heat through the movement of a fluid (liquid or gas). It involves the circulation of the fluid due to differences in temperature and density. Gravity plays a significant role in convection as it causes the denser, cooler fluid to sink and the less dense, hotter fluid to rise. This creates a convection current, facilitating the transfer of heat. Therefore, gravity is involved in convection.

Radiation:
Radiation is the transfer of heat through electromagnetic waves. It does not require a medium or direct contact between objects for heat transfer to occur. Instead, heat energy is transferred in the form of infrared radiation. Gravity does not play a part in radiation as it is a purely electromagnetic process.

Conclusion:
Among the given options, the correct answer is option 'B' - Radiation and conduction. Gravity does not play any part in radiation and conduction. It only affects convection, which involves the movement of a fluid due to differences in temperature and density.