Convection currents form due to what?

Correct answer: Thermal difference

Convection currents are movements produced by differences in temperature and density. When a material is heated, it generally becomes less dense and rises. Cooler, denser material moves downward to replace it. This repeated rising and sinking creates a circulating movement called convection. In Earth science, such movements have been used to explain forces that may influence large-scale movement inside the Earth.

Option B, thermal difference, is correct. A lunar eclipse is an astronomical event and does not serve as the general cause of convection. River floods, plant growth, and the other choices do not explain the upward and downward movement of heated material. The key idea to remember is that uneven heating produces density differences, and density differences allow convection currents to develop.