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: a man goes downstream at 10 kmph, and upstream 8 kmph. the speed of the stream is
Options: a. 0 kmph, b. 4 kmph, c. 1 kmph, d. 2.5 kmph, e. 26 kmph

Output: c


Input: Consider Input: Problem: how many 4 - digit numbers that do not contain the digits 2, 3, 4, 5, 6, or 7 are there ?
Options: a. 168, b. 176, c. 184, d. 192, e. 200

Output: d


Input: Consider Input: Problem: a certain elevator has a safe weight limit of 2,000 pounds. what is the greatest possible number of people who can safely ride on the elevator at one time with the average ( arithmetic mean ) weight of half the riders being 200 pounds and the average weight of the others being 230 pounds ?
Options: a. 7, b. 8, c. 9, d. 10, e. 11


Output: c