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 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
Example Output: b

Example Input: Problem: in what time will a train 120 m long cross an electric pole, it its speed be 121 km / hr ?
Options: a. 2.5, b. 2.7, c. 2.9, d. 3.6, e. 2.1
Example Output: d

Example Input: Problem: a grocer has a sale of rs. 3435, rs. 3920, rs. 3855, rs. 4230 and rs. 3560 for 5 consecutive months. how much sale must he have in the sixth month so that he gets an average sale of rs. 3500 ?
Options: a. 500, b. 1000, c. 6000, d. 7000, e. 2000
Example Output:
e