Final answer:
The mantle is heated through convection in the core, which leads to heat transfer by conduction.
Step-by-step explanation:
The correct answer is (D) convection in the core heats the mantle through conduction.
Convection is the process of heat transfer through the movement of mass. In Earth's interior, slow convection occurs in the mantle, where heat escapes from the core through the upward flow of warmer material and the slow sinking of cooler material. This convection in the core ultimately heats the mantle through conduction, which is the transfer of heat between two objects in direct contact with each other.