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: x does a work in 20 days. y does the same work in 40 days. in how many days they together will do the same work ?
Options: a. 10, b. 12, c. 20, d. 30, e. 13.33

Ex Output:
e


Ex Input:
Problem: a fort had provision of food for 150 men for 45 days. after 10 days, 25 men left the fort. find out the number of days for which the remaining food will last.
Options: a. 44, b. 42, c. 40, d. 38, e. 36

Ex Output:
b


Ex Input:
Problem: if the sides of a cube are in the ratio 9: 7. what is the ratio of their diagonals ?
Options: a. 4: 3, b. 16: 9, c. 9: 7, d. 3: 4, e. 3: 8

Ex Output:

c