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: if the radius of a cylinder is made 3 times and so is the height, what is the new volume of the cylinder divided by the old one ?
Options: a. 27., b. 2., c. 6., d. 4., e. 10.
Example Output: a

Example Input: Problem: a fort had provision of food for 150 men for 45 days. after 10 days, 25 men left the fort. find out the number of days for which the remaining food will last.
Options: a. 44, b. 42, c. 40, d. 38, e. 36
Example Output: b

Example Input: Problem: in a room with 6 people, 4 people have exactly 1 friend in the room and 3 people have exactly 2 friends in the room ( assuming that friendship is a mutual relationship, i. e. if jane is paul ' s friend, paul is jane ' s friend.. if two individuals are selected from the room at random, what is the probability that those two individuals are not friends ?
Options: a. 5 / 21, b. 3 / 7, c. 4 / 7, d. 5 / 7, e. 16 / 15
Example Output:
e