Could be false. This answer choice confuses sufficiency for necessity. We know that literature professors have years of special training, but we don’t know whether everyone with this training is able to judge the greatness of literary works accurately. Years of training are necessary for judging greatness, but not sufficient.

Could be false. We don’t have any information in the stimulus about all people who are not literature professors. As shown on our diagram, there are no necessary conditions attached to the condition of not being a literature professor. If you liked this, you probably thought people who are not literature professors cannot have years of specialized training. But this confuses sufficiency and necessity. It's possible someone is not a literature professor but still has years of specialized training.

Could be false. The stimulus does not make a value judgment about what should occur.

Could be false. As shown on our diagram, we can infer that among the reading public, most people are not literature professors. But this tells us nothing about how many literature professors belong to the reading public. It’s still possible that some, or even all, literature professors belong to the reading public.

Must be true. The vast majority of the reading public lacks years of special training, which means they can’t judge the greatness of literary works accurately.