If the angles of depression of the upper and lower ends of a lamp post the top of a hill of height $h$ meters are $\alpha$ and $\beta$ respectively, then the height of the lamp post is equal to :

Question

( A ) $h \sin \alpha \sin \beta$
( B ) $h \sin ( \beta - \alpha)$
( C ) $h \cos ( \beta - \alpha)$
( D ) $-\frac{h \sin (\beta - \alpha)}{\cos \alpha \sin \beta}$