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: calculate the circumference of a circular field whose radius is 8 centimeters . 
Options: a ) 17 π cm , b ) 18 π cm , c ) 1 π cm , d ) 16 π cm , e ) 6 π cm
Example Output: d

Example Input: Problem: r is the set of positive even integers less than 20 , and s is the set of the squares of the integers in r . how many elements does the intersection of r and s contain ? 
Options: ['a ) none', 'b ) two', 'c ) three', 'd ) five', 'e ) seven']
Example Output: c

Example Input: Problem: find the cost of fencing around a circular field of diameter 26 m at the rate of rs . 1.50 a meter ? 
Options: a ) 122.55 , b ) 132 , c ) 156 , d ) 158 , e ) 267
Example Output:
a