Four point size bodies each of mass m are fixed at four corners of light square frame of side length 1m. The radius of gyration of these four bodies about an axis perpendicular to the plane of frame passing through its centre is

• A

  $\sqrt{2}$

• B

  2

• C

  $\frac{1}{\sqrt{2}}$

• D

  $\frac{1}{2}$