One Star in a Binary Will Almost Always Become a Red

One star in a binary will almost always become a red giant before the other because:

A) one star is always larger than the other.
B) binaries always have one star twice as massive as the other.
C) small differences in main-sequence masses yield large differences in main-sequence lifetimes.
D) the more massive binary star always gets more mass from the less massive binary star when both are main-sequence stars.