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 light flashes every 30 seconds, how many times will it flash in ? of an hour ?
Options: a. 550, b. 600, c. 650, d. 700, e. 120
Example Output: e

Example Input: Problem: the area of a square field is 625 km 2. how long will it take for a horse to run around at the speed of 25 km / h ?
Options: a. 12 h, b. 10 h, c. 8 h, d. 4 h, e. none of these
Example Output: d

Example Input: Problem: two trains 111 meters and 165 meters in length respectively are running in opposite directions, one at the rate of 40 km and the other at the rate of 50 kmph. in what time will they be completely clear of each other from the moment they meet ?
Options: a. 11.04, b. 10.0, c. 6.85, d. 5.85, e. 6.15
Example Output:
a