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.

Ex Input:
Problem: two trains of length 100 meters and 200 meters are 450 meters apart. they are moving towards each other on parallel tracks, at speeds of 90 km / h and 72 km / h. after how many seconds will the trains meet ?
Options: a. 6, b. 8, c. 10, d. 12, e. 14

Ex Output:
c


Ex Input:
Problem: what is the least number of squares tiles required to pave the floor of a room 15.17 m long and 9.02 m broad ?
Options: ['a. 814', 'b. 266', 'c. 287', 'd. 999', 'e. 661']

Ex Output:
a


Ex Input:
Problem: the average of first 20 natural numbers is ?
Options: a. 10.5, b. 11.4, c. 5.3, d. 5.9, e. 5.1

Ex Output:

a