Two Bodies, One of Mass M and the Other of Mass

Multiple Choice

Two bodies, one of mass M and the other of mass m, are subject only to their mutual gravitational attraction. One possible motion is for both of them to revolve in concentric circles about their center of mass. What is the connection between the period of the revolutions and the separation R between the two bodies in this case?

A) 2πR^3/2/[G(M+m) ]^1/2
B) 2πR^3/2(M+m) ^1/2/(GMm) ^1/2
C) 2πR^3/2(M+m) ^1/2/[G(M²+m²) ]^1/2
D) 2πR^3/2(M+m) /(G) ^1/2 (Mm) ^3/4
E) 4πR^3/2(M+m) /(G) ^1/2 (Mm) ^3/4