Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Ex Input:
Problem: if 12 machine can finish a job in 40 days, then how many more machines would be needed to finish the job in one - fourth less time ?
Options: a. a. 4, b. b. 8, c. c. 10, d. d. 12, e. e. 16

Ex Output:
a

Ex Input:
Problem: the average of first six prime numbers greater than 20 is ?
Options: a. 10, b. 20, c. 30, d. 40, e. 34

Ex Output:
e

Ex Input:
Problem: a girl multiplies 987 by a certain number and obtains 559981 as her answer. if in the answer, both 9 ' s are wrong but the other digits are correct, then the correct answer will be
Options: a. 553681, b. 555181, c. 555681, d. 556581, e. none of these

Ex Output:
c