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: set a contains all the even numbers between 2 and 50 inclusive. set b contains all the even numbers between 62 and 110 inclusive. what is the difference between the sum of elements of set b and the sum of the elements of set a ?
Options: a. 1500, b. 3100, c. 4400, d. 6200, e. 7400

Ex Output:
a


Ex Input:
Problem: the population of a town increases 25 % and 40 % respectively in two consecutive years. after the growth the present population of the town is 1750. then what is the population of the town 2 years ago ?
Options: a. a. 750, b. b. 800, c. c. 850, d. d. 900, e. e. 950

Ex Output:
b


Ex Input:
Problem: the spherical ball of lead 3 cm in diameter is melted and recast into 3 spherical balls. the diameters of two of these are 1 1 / 2 cm and 2 cm respectively. the diameter of third ball is ?
Options: a. 2.8, b. 2.5, c. 2.2, d. 2.0, e. 2.1

Ex Output:

b