Boron found in nature has an atomic weight of 10.811 and is made up of the isotopes 10B (mass 10.013 amu) and 11B (mass 11.0093 amu). What percentage of naturally occurring boron is made up of 10B and 11B respectively?
a. 30:70
b. 25:75
c. 20:80
d. 15:85