How can the cyclic movement of material in convection current be understood correctly?

Correct answer: Heating and rising, spreading, cooling and sinking

A convection current is a continuous cycle caused by heating and cooling. Material heated at depth becomes less dense and rises. Near the upper part, it spreads sideways and gradually loses heat. After cooling, it becomes denser and sinks again. At depth it may be heated once more, allowing the cycle to continue. Option A presents this sequence in the correct order: heating and rising, spreading, cooling, and sinking.

The other choices omit an essential part or reverse the physical process. Cooling generally makes the material denser, so cooling and rising is not the normal sequence. Material does not simply remain fixed, and a convection cycle cannot consist only of upward movement because the return downward flow is necessary. In the mantle, these movements are very slow and occur over long geological periods, but the order remains the same. The supplied answer A is therefore consistent with the basic convectional-current theory.