Boron (B) has two Isotopes, boron-10 and boron-11. The atomic weight of boron is the
A. combined masses of boron-10 and boron-11
B. average number of neutrons in boron-10 and boron-11
C. weighted average of the masses of boron-10 and boron-11
D. mass of boron-10 minus the mass of boron-11