What are the two layers below earth's surface in which convection takes place?

Convection occurs in the Mantle and the Outer Core.

The two layers below Earth's surface in which convection takes place are mantle and outer core.
Convection is a form of heat transfer which also includes energy. This happens below Earth's surface in its mantle, which is its interior, and is found between the crust and outer core. And the outer core is fluid and consists mostly of nickel and iron and can be found below the mantle.

Why you put last one a? i think is b.