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: the average of first 10 natural numbers is ?
Options: a. 5.6, b. 5.5, c. 5.1, d. 5.8, e. 5.2
Example Output: b

Example Input: Problem: a monkey ascends a greased pole 10 meters high. he ascends 2 meters in the first minute and then slips down 1 meter in the alternate minute. if this pattern continues until he climbs the pole, in how many minutes would he reach at the top of the pole ?
Options: a. 10 th minute, b. 21 st minute, c. 17 th minute, d. 22 nd minute, e. 13 th minute
Example Output: c

Example Input: Problem: the perimeter of a rhombus is 68 cm and one of its diagonals is 16 cm. find its area ?
Options: a. 290, b. 240, c. 2870, d. 289, e. 292
Example Output:
b