What process provides the source or generates the thermal heat that leads to hotspots and melts the earth's crust?

Hint: This is a review of HE#1 & HE#2 material... Please consider the definition of a hotspot. It is widely believed that hotspots form where the inner core makes contact with the mantle or lowermost asthenosphere.

Select one:

a. Radioactivity in the core

b. Conduction in the lithosphere

c. Convection in the asthenosphere

d. Radiation from the sun