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 man goes downstream at 10 kmph, and upstream 8 kmph. the speed of the stream is
Options: a. 0 kmph, b. 4 kmph, c. 1 kmph, d. 2.5 kmph, e. 26 kmph
Example Output: c

Example Input: Problem: there are 750 male and female participants in a meeting. half the female participants and one - quarterof the male participants are democrats. one - third of all the participants are democrats. how many of the democrats are female ?
Options: a. 75, b. 100, c. 125, d. 175, e. 225
Example Output: c

Example Input: Problem: a and b go around a circular track of length 600 m on a cycle at speeds of 36 kmph and 54 kmph. after how much time will they meet for the first time at the starting point ?
Options: a. 120, b. 775, c. 555, d. 288, e. 278
Example Output:
a