what is applied directly to the CPU?

When installing a new CPU, what is applied directly to the CPU?

A.
Cooling liquid.

B.
Thermal compound.

C.
A heat sink.

D.
A fan.

Explanation:
Thermal grease (also called thermal compound, heat paste, thermal paste, or heat sink
compound) is a substance that increases thermal conductivity between the surfaces of two or
more objects. In electronics, it is often used to aid a component’s thermal dissipation via a heat
sink.