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 9 / ( 1 + 4 / x ) = 1, then x =
Options: a. 3, b. 1 / 2, c. 1 / 3, d. - 1 / 3, e. - 3

Ex Output:
b


Ex Input:
Problem: heinz produces tomato puree by boiling tomato juice. the tomato puree has only 20 % water while the tomato juice has 90 % water. how many liters of tomato puree will be obtained from 25 litres of tomato juice ?
Options: a. 2.8 liters., b. 3.125 liters., c. 8.5 liters., d. 2.6 liters., e. 2.1 liters.

Ex Output:
b


Ex Input:
Problem: there are 25 balls in a jar. you take out 5 blue balls without putting them back inside, and now the probability of pulling out a blue ball is 1 / 5. how many blue balls were there in the beginning ?
Options: a. 12., b. 9., c. 8., d. 7., e. 6.

Ex Output:

b