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.

Ex Input:
Problem: if the sides of a cube are in the ratio 5: 3. what is the ratio of their diagonals ?
Options: ['a. 5: 9', 'b. 9: 3', 'c. 5: 4', 'd. 3: 5', 'e. 5: 3']

Ex Output:
e


Ex Input:
Problem: if the population of a certain country increases at the rate of one person every 15 seconds, by how many persons does the population increase in 25 minutes ?
Options: a. 80, b. 100, c. 150, d. 240, e. 300

Ex Output:
b


Ex Input:
Problem: in a certain parking lot, 4 % of the cars are towed for parking illegally. however 80 % of the cars which are parked illegally are not towed. what percentage of cars in the parking lot are parked illegally ?
Options: a. 20 %, b. 25 %, c. 30 %, d. 35 %, e. 40 %

Ex Output:

a