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: ravi purchased a refrigerator and a mobile phone for rs. 15000 and rs. 8000 respectively. he sold the refrigerator at a loss of 5 percent and the mobile phone at a profit of 10 percent. overall he make a.
Options: a. 50, b. 288, c. 27, d. 200, e. 881

Ex Output:
a

Ex Input:
Problem: a train 250 m long running at 72 kmph crosses a platform in 25 sec. what is the length of the platform ?
Options: a. 150 m, b. 200 m, c. 250 m, d. 270 m, e. 300 m

Ex Output:
c