Boron has two isotopes $_5B^{10}$ and $_5B^{11}$. If atomic weight of Boron is 10.81 then ratio of $_5B^{10}$ to $_5B^{11}$ in nature will be :

Question

( A ) 19 : 81
( B ) 20 : 53
( C ) 81 : 19
( D ) 15 : 16