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 mixture is 1 ⁄ 7 alcohol by volume and 2 ⁄ 7 water by volume, what is the ratio of the volume of alcohol to the volume of water in this mixture ?
Options: a. 4 / 2, b. 3 / 2, c. 1 / 2, d. 5 / 2, e. 7 / 2

Ex Output:
c


Ex Input:
Problem: a grocer has a sale of rs. 5420, rs. 5660, rs. 6200, rs. 6350 and rs. 6500 for 5 consecutive months. find the sale he should have in the sixth month, so that he gets an average sale of rs. 6400 ?
Options: a. rs. 5870, b. rs. 8270, c. rs. 6020, d. rs. 6850, e. none of these

Ex Output:
b


Ex Input:
Problem: a man sitting in a train which is travelling at 80 kmph observes that a goods train, travelling in opposite direction, takes 9 seconds to pass him. if the goods train is 280 m long, find its speed ?
Options: a. 52 kmph., b. 62 kmph., c. 72 kmph., d. 80 kmph., e. 32 kmph.

Ex Output:

e