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.

Input: Consider Input: Problem: what is the units digit of ( 3 ^ 13 ) ( 4 ^ 13 ) ?
Options: a. 2, b. 4, c. 6, d. 7, e. 8

Output: a


Input: Consider Input: Problem: when x is multiplied by 3, the result is 10 more than the result of subtracting x from 26. what is the value of x ?
Options: a. - 4, b. 9, c. 11, d. 13, e. 22

Output: b


Input: Consider Input: Problem: one man adds 3 liters of water to 12 liters of milk and another 4 liters of water to 10 liters of milk. what is the ratio of the strengths of milk in 2 mixtures ?
Options: a. 11: 21, b. 15: 33, c. 28: 25, d. 3: 2, e. 31: 33


Output: c