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: in what time will a train 50 m long cross an electric pole, it its speed be 360 km / hr ?
Options: a. 0.25, b. 0.5, c. 1.5, d. 2.5, e. 3.5
Example Output: b

Example Input: Problem: excluding stoppages, the average speed of a bus is 60 km / hr and including stoppages, the average speed of the bus is 40 km / hr. for how many minutes does the bus stop per hour ?
Options: a. 18 min, b. 17 min, c. 19 min, d. 20 min, e. 21 min
Example Output: d

Example Input: Problem: find the value of 72517 x 9999 = m ?
Options: a. 345434667, b. 246465757, c. 465767867, d. 725097483, e. 645354643
Example Output:
d