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: two positive integers differ by 4, and sum of their reciprocals is 2. then one of the numbers is
Options: a. a. 3, b. 2, c. c. 5, d. d. 21, e. e. 28

Ex Output:
b


Ex Input:
Problem: a company produces 50000 bottles of water everyday. if a case can hold 25 bottles of water. how many cases are required by the company to hold its one day production
Options: a. 2000, b. 4500, c. 5000, d. 8000, e. 9000

Ex Output:
a


Ex Input:
Problem: arnold and danny are two twin brothers that are celebrating their birthday. the product of their ages today is smaller by 15 from the product of their ages a year from today. what is their age today ?
Options: a. 2., b. 4., c. 5., d. 7., e. 9.

Ex Output:

d