Protostars with Masses of More Than About 4 Times the Mass

Protostars with masses of more than about 4 times the mass of the Sun maintain approximately constant luminosity through their pre-main-sequence lifetimes. This is because:

A) the star contracts as its surface temperature decreases, and the change in surface area compensates for the change in energy emitted per unit area.
B) the surface temperature increases as the star contracts, and the change in energy emitted per unit area compensates for the change in surface area.
C) they contract too rapidly for their temperature and luminosity to change significantly.
D) they are too massive to contract significantly, thus keeping luminosity constant.