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: how many integers v are prime numbers in the range 200 < v < 220 ?
Options: a. 1, b. 2, c. 3, d. 4, e. 5
Example Output: a

Example Input: Problem: i flew my tiny seaplane to visit my mother. on the flight up, i flew at 96 mph. on the way home, i flew 88 mph. what was my average speed for the trip ?
Options: a. 198 mph, b. 110 mph, c. 92 mph, d. 100 mph, e. 99 mph
Example Output: c

Example Input: Problem: the grade point average of the entire class is 90. if the average of one third of the class is 96, what is the average of the rest ?
Options: a. 92, b. 89, c. 88, d. 87, e. 86
Example Output:
d