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: in 10 years, a will be twice as old as b was 10 years ago. if a is now 5 years older than b the present age of b is
Options: a. 37, b. 38, c. 39, d. 35, e. 41

Ex Output:
d


Ex Input:
Problem: kathleen can paint a room in 4 hours, and anthony can paint an identical room in 5 hours. how many hours would it take kathleen and anthony to paint both rooms if they work together at their respective rates ?
Options: a. 8 / 15, b. 40 / 9, c. 15 / 8, d. 9 / 4, e. 15 / 4

Ex Output:
b


Ex Input:
Problem: the duplicate ratio of 4: 5 is ?
Options: a. 1: 2, b. 1: 4, c. 1: 8, d. 1: 18, e. 16: 25

Ex Output:

e