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: the average age of a family of 5 members is 20 years. if the age of the youngest member be 10 years then what was the average age of the family at the time of the birth of the youngest member ?
Options: a. 13.5, b. 14, c. 15, d. 12.5, e. none

Ex Output:
d


Ex Input:
Problem: if y exceeds x by 25 %, then x is less than y by ?
Options: a. 28 %, b. 21 %, c. 20 %, d. 30 %, e. 29 %

Ex Output:
c


Ex Input:
Problem: in a group of 28 junior high school students, 5 take french, 10 take spanish, and 4 take both languages. the students taking both french and spanish are not counted with the 7 taking french or the 10 taking spanish. how many students are not taking either french or spanish ?
Options: a. 7, b. 13, c. 9, d. 12, e. 10

Ex Output:

b