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 a / b = 4 / 3, then ( 3 a + 2 b. / ( 3 a - 2 b. = ?
Options: a. 6, b. 3, c. 5, d. - 1, e. none

Ex Output:
b


Ex Input:
Problem: the area of a square field is 625 km 2. how long will it take for a horse to run around at the speed of 25 km / h ?
Options: a. 12 h, b. 10 h, c. 8 h, d. 4 h, e. none of these

Ex Output:
d


Ex Input:
Problem: two trains are approaching each other at 60 mph each. the length of each train is 1 / 6 miles. when the two locomotives ( engines ) meet, how many seconds will it take for them to pass each other completely ?
Options: a. 8 sec, b. 11 sec, c. 12 sec, d. 10 sec, e. 15 sec

Ex Output:

d