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: two trains of equal length are running on parallel lines in the same directions at 46 km / hr. and 36 km / hr. the faster trains pass the slower train in 72 seconds. the length of each train is :
Options: a. 82 m, b. 50 m, c. 72 m, d. 100 m, e. none of these
Example Output: d

Example Input: Problem: the smallest number which when diminished by 2, is divisible by 12, 16, 18, 21 and 28 is
Options: a. 1008, b. 1010, c. 1022, d. 1032, e. 1043
Example Output: b

Example Input: Problem: the area of sector of a circle whose radius is 12 metro and whose angle at the center is 30 ° is ?
Options: ['a. 35 m 2', 'b. 36 m 2', 'c. 37 m 2', 'd. 38 m 2', 'e. 40 m 2']
Example Output:
c