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: if 21 lines are drawn in a plane such that no two of them are parallel and no three are concurrent , then in how many points do they intersect ?
Options: a ) 150 , b ) 170 , c ) 190 , d ) 210 , e ) 230
Example Output: d

Example Input: Problem: the sum of two consecutive integers is 61 . find the numbers .
Options: a ) 17 , 18 , b ) 30,31 , c ) 5 , 6 , d ) 1 , 2 , e ) 8 , 9
Example Output: b

Example Input: Problem: a and b can do a piece of work in 48 days , a and c can do it in 60 days , b and c can do it 72 days . in what time can c alone do it ?
Options: a ) 84 days , b ) 84 days , c ) 85 days , d ) 87 days , e ) 89 days
Example Output:
c