Why Does the Core of the Sun Contain More Helium

Why does the core of the Sun contain more helium and less hydrogen than the surface of the Sun?

A) The hydrogen has been lifted out of the core by the Sun's magnetic field.
B) Helium is heavier than hydrogen and has sunk toward the center in a process of chemical differentiation.
C) Helium condenses more easily, so when the Sun was forming the core became helium-rich; vast quantities of hydrogen were added only after the core became massive enough.
D) Thermonuclear reactions have converted much of the original hydrogen in the core into helium.