In this task, you need to answer the given multiple-choice question on geometry. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: the radius of a sphere is increased by 10 % . the surface area increases by ? 
Options: ['a ) 21 %', 'b ) 31 %', 'c ) 41 %', 'd ) 51 %', 'e ) none of these']
Example Output: a

Example Input: Problem: how many odd numbers between 10 and 1,200 are the squares of integers ? 
Options: a ) 12 , b ) 13 , c ) 14 , d ) 15 , e ) 16
Example Output: e

Example Input: Problem: the perimeter of an equilateral triangle is 60 . if one of the sides of the equilateral triangle is the side of an isosceles triangle of perimeter 50 , then how long is the base of isosceles triangle ? 
Options: a ) 5 , b ) 10 , c ) 15 , d ) 20 , e ) 25
Example Output:
b