Given the task definition and input, reply with output. 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.

Problem: 2,7, 17,3, 11,19, 5,13, __
Options: a. 20, b. 21, c. 22, d. 23, e. 24

d