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: a box contains 10 tablets of medicine a and 10 tablets of medicine b. what is the least number of tablets that should be taken from the box to ensure that at least two tablets of each kind are among the extracted.
Options: a. 12, b. 15, c. 17, d. 19, e. 21
a