JEE Math Practice Question

Let a vertical tower $$A B$$ of height $$2 h$$ stands on a horizontal ground. Let from a point $$P%$$ on the ground a man can see upto height $$h$$ of the tower with an angle of elevation $$2 \alpha$$. When from $$P$$, he moves a distance $$d$$ in the direction of $$\overrightarrow{A P}$$, he can see the top $$B$$ of the tower with an angle of elevation $$\alpha$$. If $$d=\sqrt{7} h$$, then $$\tan \alpha$$ is equal to

1. A.$$\sqrt{5}-2$$
2. B.$$\sqrt{3}-1$$
3. C.$$ \sqrt{7}-2$$
4. D.$$\sqrt{7}-\sqrt{3}$$