A vertical tower stands on a horizontal plane and is surmounted by a vertical flag staff of height h. At a point on the plane, the angle of elevation of the bottom of the flag staff is $$\alpha$$ and that of the top of the flag staff is $$\beta$$. Then the height of the tower is

A

$$h \tan \alpha$$

B

$$\frac{h \tan \alpha}{\tan \beta - \tan \alpha}$$

C

$$\frac{h \tan \alpha}{\tan \alpha - \tan \beta}$$

D

None of these