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.

Input: Consider Input: Problem: a train of length 250 m crosses a bridge of length 150 m in 20 seconds. what is the speed of train ?
Options: a. 33, b. 27, c. 25, d. 22, e. 72

Output: e

Input: Consider Input: Problem: if a and b are positive real numbers, and a ^ 3 + b ^ 3 = 25, then the greatest possible value of a is between :
Options: a. 0 and 3, b. 3 and 4, c. 4 and 5, d. 5 and 7, e. 7 and 9

Output: a

Input: Consider Input: Problem: how many multiples of 4 are there between 4 and 64 ?
Options: a. 12, b. 64, c. 14, d. 16, e. 60
Output: c