Could be false. This answer choice confuses sufficiency for necessity. We know that any literary classic is worthy of serious study, but it is possible that there are other books worthy of serious study that are not literary classics.

Must be true. As shown below, worthiness of serious study is a necessary condition in order for a book to be a literary classic.

Could be false. The stimulus tells us that in order to be a literary classic, a book must be worthy of serious study. It is possible that there are some literary classics that exist, in which case there would be some literary classics that are worthy of serious study.

Could be false. Although we cannot infer that every book worthy of serious study reveals something significant about the human condition, it's possible that this is true. (If we know that All As are B, we cannot infer that All Bs are A, but it's possible that All Bs are A.).

Could be false. Although we cannot infer that every book that reveals something significant about the human condition is a literary classic, it's possible that this is true. (If we know that All As are B, we cannot infer that All Bs are A, but it's possible that All Bs are A.)