Two particles of equal mass m go round a circle of radius R under the action of their mutual gravitational attraction. The speed of each particle is

• A

  $v = \sqrt{\frac{Gm}{R}}$

• B

  $v = \sqrt{\frac{Gm}{2R}}$

• C

  $v = \frac{1}{2} \sqrt{\frac{Gm}{R}}$

• D

  $v = \sqrt{\frac{4Gm}{R}}$