In the Earth's mantle, heat is transferred in large convection currents. Within these currents,
A.
cooler rock rises and hotter rock sinks.
B.
hotter rock rises and cooler rock sinks.
C.
hotter and cooler rock sink but do not rise.

In the Earth's mantle, heat is transferred in large convection currents. Within these currents "hotter rock rises and cooler rock sinks".

Option B

Explanation:

Heat rises occur and the hotter rock gets farther away from the Earth's overheated core it starts to chill out and continues to sink back towards the Earth's overheated center where it gets reheated and also the entire procedure begins again. It's what a current in convection is.

Convection currents are part of what keeps the Earth's atmosphere through global circulation. The convection currents contribute to conditions in the air and sea. Magma travels in convection currents at Earth's mantle. The hot cores heat the above substance, allowing it to rise to the crust where it cools.