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'.

Ex Input:
Problem: what is the next number 12 13 15 17 111 113 117 119 123 129 ? 
Options: a ) 154 , b ) 220 , c ) 129 , d ) 131 , e ) 224

Ex Output:
d


Ex Input:
Problem: village x has a population of 76000 , which is decreasing at the rate of 1200 per year . village y has a population of 42000 , which is increasing at the rate of 800 per year . in how many years will the population of the two villages be equal ? 
Options: a ) 15 , b ) 17 , c ) 11 , d ) 18 , e ) 13

Ex Output:
b


Ex Input:
Problem: ele , the circus elephant , is currently 3 times older than lyn , the circus lion . in 15 years from now , lyn the circus lion will be exactly half as old as ele , the circus elephant . how old is ele today ? 
Options: a ) 40 , b ) 48 , c ) 43 , d ) 45 , e ) 41

Ex Output:

d