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: for any positive integer n, the sum of the first n positive integers equals n ( n + 1 ) / 2. what is the sum of all the integers between 100 and 200 ?
Options: a. 4545, b. 5050, c. 6525, d. 4352, e. 4652
Example Output: b

Example Input: Problem: what is the units digit of 26 ! + 50 ! + 4 ! + 4 ! ?
Options: a. 8, b. 6, c. 4, d. 2, e. 0
Example Output: a

Example Input: Problem: if the radius of a circle is increased by 20 % then the area is increased by :
Options: a. 44 %, b. 120 %, c. 144 %, d. 40 %, e. none of the above
Example Output:
a