B, C and binary stars provide centripetal force by mutual attraction, with equal period, equal angular velocity and equal centripetal force, so B is wrong and C is wrong;

A, D and binary stars provide centripetal force through mutual attraction with equal periods. According to GM12l2 = m1r1ω 2 = m2r2ω 2, the radius is:

r 1:R2 = m2:m 1 = 1:2

According to v=rω:

v 1:v2 = r 1:R2 = m2:m 1 = 1:2

Therefore, A is correct and D is wrong;

So choose: a.