The angle of elevation of the top of a building from the top and bottom of a tree are x and y respectively. If the height of the tree is h metre, then (in metre) the height of the building is

• A. <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>h cot x</center></td></tr><td align="center">cot x + cot y</td></table>
• B.
• C. <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>h cot y</center></td></tr><td align="center">cot x + cot y</td></table>
• D. <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>h cot x</center></td></tr><td align="center">cot x - cot y</td></table>
• E. <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>h cot y</center></td></tr><td align="center">cot x - cot y</td></table>