In a Cepheid Variable, What Happens to Make Its Temperature

In a Cepheid variable, what happens to make its temperature rise?

A) A layer of ionized helium absorbs photons.
B) The fusion reaction switches from hydrogen fusion to helium fusion.
C) The hydrogen fusion in the shell increases as it receives a periodic burst of convection current-carried fuel.
D) The electron degeneracy in the core refuses to allow the core to expand in response to energy generation.