If 'a' stands for the edge length of the cubic 3 systems : simple cubic, body centered cubic and face centered cubic, then the ratio of radii of the spheres in these systems will be respectively.

Question

( A ) $\frac{1}{2}a:\frac{\sqrt{3}}{4}a:\frac{1}{2\sqrt2}a$
( B ) $1a:\sqrt{3a}:\sqrt{2a}$
( C ) $\frac{1}{2}a:\sqrt{3a}:\frac{1}{\sqrt2}a$
( D ) $\frac{1}{2}a:\frac{\sqrt3}{2}:\frac{\sqrt2}{2}a$