A point O is the centre of a circle circumscribed about a triangle ABC. Then,
`O vec A sin 2 A + O vec B sin 2 B + O vec C sin 2 C ` is equal to
A. `(O vec a + O vec B + O vec C ) sin 2 A `
B. `3 vec(OG), ` where G is the centroid of triangle ABC
C. `vec 0`
D. none of these
