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.

Example Input: Problem: a trader mixes 80 kg of tea at 15 per kg with 20 kg of tea at cost price of 20 per kg. in order to earn a profit of 25 %, what should be the sale price of the mixed tea ?
Options: a. 23.75, b. 22, c. 20, d. 19.20, e. none of these
Example Output: c

Example Input: Problem: how many integers v are prime numbers in the range 200 < v < 220 ?
Options: a. 1, b. 2, c. 3, d. 4, e. 5
Example Output: a

Example Input: Problem: a man cheats while buying as well as while selling. while buying he takes 10 % more than what he pays for and while selling he gives 20 % less than what he claims to. find the profit percent, if he sells at 10 % below the cost price of the claimed weight.
Options: a. 19.81 %, b. 20 %, c. 37.5 %, d. 23.75 %, e. 37.5 %
Example Output:
d