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

Example Input: Problem: a cistern of capacity 8000 litres measures externally 3.3 m by 2.6 m by 1.2 m and its walls are 5 cm thick . the thickness of the bottom is : 
Options: a ) 90 cm , b ) 2 dm , c ) 1 m , d ) 1.1 cm , e ) none of these
Example Output: b

Example Input: Problem: circular gears p and q start rotating at the same time at constant speeds . gear p makes 10 revolutions per minute and gear q makes 40 revolutions per minute . how many seconds after the gears start rotating will gear q have made exactly 15 more revolutions than gear p ? 
Options: a ) 12 , b ) 15 , c ) 20 , d ) 24 , e ) 30
Example Output: e

Example Input: Problem: the perimeter of a semi circle is 180 cm then the radius is ? 
Options: a ) 22 , b ) 28 , c ) 35 , d ) 37 , e ) 13
Example Output:
c