During convection, hot material then moves to the side and . this circular pattern is called a convection current.

During convection, hot material then moves to the side and create a void which must be filled with new less hot material, this creates a circular pattern. This circular patter is called convection current. That is the description of the mechanism of transfer of matter and heat by convection. That is how the heat transfer in fluids (liquid and gases) and is also the force behind the motion of plates (continents) as per geologists.

The answer for this question is d. none of these