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: the mean of 50 observations is 200. but later he found that there is decrements of 34 from each observations. what is the the updated mean is ?
Options: a. 165, b. 166, c. 190, d. 198, e. 199

Ex Output:
b


Ex Input:
Problem: two trains of length 100 meters and 200 meters are 450 meters apart. they are moving towards each other on parallel tracks, at speeds of 90 km / h and 72 km / h. after how many seconds will the trains meet ?
Options: a. 6, b. 8, c. 10, d. 12, e. 14

Ex Output:
c


Ex Input:
Problem: if the cost price of 50 articles is equal to the selling price of 40 articles, then the gain or loss percent is ?
Options: a. 33 %, b. 29 %, c. 25 %, d. 55 %, e. 39 %

Ex Output:

c