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'.

Input: Consider 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

Output: d


Input: Consider Input: Problem: 998 x 998 = ? 
Options: a ) 996000 , b ) 1000000 , c ) 996004 , d ) 4000 , e ) 996008

Output: c


Input: Consider Input: Problem: find the least number of complete years in which a sum of money put out at 15 % compound interest will be more than double of itself ? 
Options: a ) 5 , b ) 6 , c ) 7 , d ) 8 , e ) 9


Output: a