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

1. A
   $\frac{1}{2}a:\frac{\sqrt{3}}{4}a:\frac{1}{2\sqrt{2}}a$
2. B
   $\frac{1}{2}a:\sqrt{3}a:\frac{1}{\sqrt{2}}a$
3. C
   $\frac{1}{2}a:\frac{\sqrt{3}}{2}a:\frac{\sqrt{2}}{2}a$
4. D
   $1a:\sqrt{3}a:\sqrt{2}a$