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

Example Input: Problem: cost is expressed by the formula tb ^ 4 . if b is doubled , the new cost is what percent of the original cost ?
Options: a ) 200 , b ) 600 , c ) 800 , d ) 1600 , e ) 50
Example Output: d

Example Input: Problem: the sum of three consecutive multiples of 3 is 108 . what is the largest number ?
Options: a ) 36 , b ) 39 , c ) 33 , d ) 30 , e ) 42
Example Output: b

Example Input: Problem: the cost per unit of electricity during a 4 year period is as follows : year 1 , $ 3 per unit ; year 2 , $ 4 per unit ; year 3 , $ 5 per unit ; year 4 , $ 6 per unit . if a factory spent equal dollars on electricity each year , what was the average cost of a unit of electricity during the 4 year period ?
Options: a ) $ 4.31 , b ) $ 4.51 , c ) $ 4.21 , d ) $ 5.21 , e ) $ 5.61
Example Output:
c