Alison Bender works for an accounting firm. To make sure her work does not contain errors, her manager randomly checks on her work. Alison recently filled out 12 income tax returns for the company’s clients. Unknown to anyone, 2 of these 12 returns have minor errors. Alison’s manager randomly selects 3 returns from these 12 returns. Find the probability that
a. Exactly 1 of them contains errors.
b. None of them contains errors.
c. Exactly 2 of them contain errors.