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.

Example Input: Problem: a train 150 m long is running at a speed of 68 kmph. how long does it take to pass a man who is running at 8 kmph in the same direction as the train ?
Options: a. 2 sec, b. 6 sec, c. 8 sec, d. 9 sec, e. 5 sec
Example Output: d

Example Input: Problem: the present worth of rs. 2310 due years hence, the rate of interest being 15 % per annum, is :
Options: a. rs. 1440, b. rs. 1750, c. rs. 1680, d. rs. 1840, e. none of these
Example Output: c

Example Input: Problem: what distance will be covered by a bus moving at 126 kmph in 10 seconds ?
Options: a. 287, b. 600, c. 350, d. 276, e. 207
Example Output:
c