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.

Ex 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

Ex Output:
b

Ex Input:
Problem: michelle deposited a certain sum of money in a savings account on july 1 st, 2007. she earns an 14 % interest compounded semiannually. the sum of money in the account on december 31 st, 2009 is approximately what percent of the initial deposit ?
Options: a. 117 %, b. 120 %, c. 121 %, d. 138 %, e. 145 %

Ex Output:
d

Ex Input:
Problem: difference between the length & breadth of a rectangle is 30 m. if its perimeter is 300 m, then its area is ? ? we have: ( l - b. = 30 and 2 ( l + b. = 300 or ( l + b. = 150 ?
Options: a. 3: 5, b. 2: 3, c. 3: 6, d. 3: 4, e. 3: 2

Ex Output:
e