Two stars of masses $$M_1=M_S$$ and $$M_2=15M_S$$, where $$M_S$$ is the mass of the Sun, form a binary system. The stars are revolving round each other, always being at a separation of $$d=4\ \text{AU}$$ between them(1 AU is distance of the Earth from the Sun), move in circular orbits about their center of mass. The period of revolution of each star is

A

$$1\ \text{year}$$

B

$$2\ \text{years}$$

C

$$4\ \text{years}$$

D

$$8\ \text{years}$$