The height at which the acceleration due to gravity becomes $\frac{g}{9}$ (where g = the acceleration due to gravity on the surace of the earth) in terms of R, the radius of the earth is

Question

( A ) $\sqrt{2}R$
( B ) $2R$
( C ) $\frac{R}{2}$
( D ) $\frac{R}{\sqrt{2}}$