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: cereal a is 10 % sugar by weight, whereas healthier but less delicious cereal b is 2 % sugar by weight. to make a delicious and healthy mixture that is 3 % sugar, what should be the ratio of cereal a to cereal b, by weight ?
Options: a. 2: 9, b. 2: 7, c. 1: 7, d. 1: 4, e. 1: 3

Ex Output:
c


Ex Input:
Problem: if a person walks at 25 km / hr instead of 10 km / hr, he would have walked 20 km more. the actual distance traveled by him is :
Options: a. 50 km, b. 56 km, c. 13.3 km, d. 70 km, e. 80 km

Ex Output:
c


Ex Input:
Problem: in a class of 32 students, 12 enrolled for both english and german. 22 enrolled for german. if the students of the class enrolled for at least one of the two subjects, then how many students enrolled for only english and not german ?
Options: a. 30, b. 10, c. 18, d. 28, e. 32

Ex Output:

b