A contact binary star system consists of:

A. Two stars that do not fill their Roche lobes

B. A giant star that fills its Roche lobe and transfers mass to the other star

C. Two giant stars that fill their Roche lobes, creating a common envelope

D. A giant star that fills it Roche lobe and transfers mass to a white dwarf

E. A giant star that fills it Roche lobe and transfers mass to a neutron star

F. A giant star that fills it Roche lobe and transfers mass to a black hole