Task: Question Answering
Input (English): Question: The number of diagonals of a polygon of n sides is given by the formula f=n(n-3)/2. If a polygon has twice as many diagonals as sides, how many sides does it have?

 Option A:  3

 Option B:  5

 Option C:  6

 Option D:  7

 Option E:  8
Output (English): Option B