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 taps a and b can fill a cistern in 12 minutes and 18 minutes respectively. they are turned on at the same time. if the tap a is turned off after 4 minutes, how long will tap b take to fill the rest of the cistern ?
Options: a. 8 min., b. 9 min., c. 10 min., d. 7 min., e. none of these
Example Output: a

Example Input: Problem: a no. when divided by 281 gives a remainder 160, what remainder will be obtainedby dividingthe same no. 21 ?
Options: a. 21, b. 22, c. 23, d. 24, e. 25
Example Output: a

Example Input: Problem: when positive integer k is divided by 5, the remainder is 2. when k is divided by 6, the remainder is 5. if k is less than 38, what is the remainder when k is divided by 7 ?
Options: a. 2, b. 4, c. 3, d. 5, e. 6
Example Output:
c