A tower stands at the centre of a circular park. $$A$$ and $$B$$ are two points on the boundary of the park such that $$AB(= a)$$ subtends an angle of $$60^\circ$$ at the foot of the tower, and the angle of elevation of the top of the tower from $$A$$ or $$B$$ is $$30^\circ$$. The height of the tower is

A

$$\frac{2a}{\sqrt{3}}$$

B

$$2a\sqrt{3}$$

C

$$\frac{a}{\sqrt{3}}$$

D

$$a\sqrt{3}$$