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.

[Q]: Problem: when positive integer n is divided by 7, the remainder is 1. when n is divided by 11, the remainder is 5. what is the smallest positive integer k such that k + n is a multiple of 77 ?
Options: a. 2, b. 4, c. 6, d. 8, e. 10
[A]: c


[Q]: Problem: a train running at the speed of 20 km / hr crosses a post in 10 seconds. what is the length of the train ?
Options: a. 150, b. 250, c. 415, d. 200, e. 312
[A]: d


[Q]: Problem: if shares of two persons in profits are rs. 600 and rs. 1000 then ratio of their capitals is
Options: a. 3: 5, b. 2: 3, c. 4: 3, d. 1: 3, e. 1: 2
[A]:
a