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 Q]: Problem: a bag contains 10 green and 8 white balls. if two balls are drawn simultaneously, the probability that both are of the same colour is
Options: a. 8 / 15, b. 21 / 44, c. 3 / 5, d. 11 / 15, e. 7 / 15
[EX A]: b

[EX Q]: Problem: in a room filled with 6 people, all 6 people have exactly 1 sibling in the room. if two individuals are selected from the room at random, what is the probability that those two individuals are not siblings ?
Options: a. 3 / 5, b. 4 / 5, c. 5 / 6, d. 5 / 12, e. 7 / 12
[EX A]: b

[EX Q]: Problem: the population of a bacteria colony doubles every day. if it was started 10 days ago with 2 bacteria and each bacteria lives for 12 days, how large is the colony today ?
Options: a. 512, b. 768, c. 1024, d. 2048, e. 4096
[EX A]:
d