Task: Question Answering
Input (English): Question: Consider a quarter of a circle of radius 81. Let r be the radius of the circle inscribed in this quarter of a circle. Find r.

 Option A: 86*(sqr2 -1

 Option B: 88*(sqr3 -1

 Option C: 4*(sqr7 - 1

 Option D: 81* (sqr2 -1

 Option E: None of these
Output (English): Option D