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 price of a certain painting increased by 30 % during the first year and decreased by 15 % during the second year. the price of the painting at the end of the 2 - year period was what percent of the original price ?
Options: a. 102 %, b. 105 %, c. 110.5 %, d. 112.5 %, e. 100 %

Ex Output:
c


Ex Input:
Problem: cathy and jim begin running at the same time and they start at the same place on a straight path. cathy runs at 10 miles per hour, and jim runs at 6 miles per hour. after 18 minutes, cathy stops to stretch. if it takes cathy 27 minutes to stretch and jim continues to run during this time, how many minutes will it take cathy to catch up to jim ?
Options: a. 20.5, b. 21.5, c. 22.5, d. 23.5, e. 24.5

Ex Output:
c


Ex Input:
Problem: if a mixture is 2 ⁄ 7 alcohol by volume and 3 ⁄ 7 water by volume, what is the ratio of the volume of alcohol to the volume of water in this mixture ?
Options: a. 3, b. 1 / 3, c. 2 / 3, d. 3 / 5, e. 4 / 5

Ex Output:

c