What three processes or forces
combine to set convection
currents in motion?

There are three types of heat transfer: radiation, conduction, and convection. Heating and cooling of the fluid, changes in the fluid's density, and the force of gravity combine to set convection currents in motion.

Explanation:

Three factors contribute to set convection currents in motion: 1. heating and cooling of the fluid, 2. changes in the fluid’s density, and 3. force of gravity

Explanation:

b. lithosphere, asthenosphere, mesosphere   is the answer most likely