What must happen for heat to be transferred by convection?

The heat transfer by convection requires a solid-fluid interface, a temperature difference between the solid surface and the surrounding fluid and a motion of the fluid. The process of heat transfer by convection would occur when there is a movement of macro-particles of the fluid in space from a region of higher temperature to lower temperature.

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answer; i believe that the correct answer is (a); a large rock being weathered by wind and rain;