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 5 a = 3125, then the value of 5 ( a - 3 ) is :
Options: a. 25, b. 125, c. 625, d. 1625, e. none of these

Ex Output:
a


Ex Input:
Problem: what least number should be added to 1057, so that the sum is completely divisible by 23
Options: a. a. 4, b. b. 1, c. c. 2, d. d. 3, e. e. 5

Ex Output:
b


Ex Input:
Problem: an empty fuel tank is filled with brand z gasoline. when the tank is 3 / 4 empty, it is filled with brand y gasoline. when the tank is half empty again, it is filled with brand z gasoline. when the tank is half empty again, it is filled with brand y gasoline. at this time, what percent of the gasoline in the tank is brand z ?
Options: a. 40 %, b. 41 %, c. 43.75 %, d. 42 %, e. 44 %

Ex Output:

c