A man standing on the bank of a river observes that the angle of elevation of the top of a tree just on the opposite bank is 60 . But angle of elevation is 30 from a point which is at a distance 20 3 ft away from the bank. Then the height of the tree is :

• A. 60 ft
• B. 45 ft
• C. 30 ft
• D. 15 ft