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.
--------
Question: Problem: in what time will a railway train 50 m long moving at the rate of 36 kmph pass a telegraph post on its way ?
Options: a. 5 sec, b. 4 sec, c. 3 sec, d. 6 sec, e. 1 sec

Answer: a


Question: Problem: a cyclist bikes x distance at 8 miles per hour and returns over the same path at 10 miles per hour. what is the cyclist ' s average rate for the round trip in miles per hour ?
Options: a. 8.1, b. 8.9, c. 8.6, d. 8.3, e. 9.0

Answer: b


Question: Problem: find the average of the first 19 natural numbers ?
Options: a. 8, b. 9, c. 10, d. 11, e. 12

Answer:
c