Critic: To be a literary classic a book must reveal something significant about the human condition. Furthermore, nothing that is unworthy of serious study reveals anything significant about the human condition.
Summary
To be a literary classic, a book must reveal something significant about the human condition. Furthermore, to reveal something significant about the human condition, it must be worthy of serious study.
Notable Valid Inferences
To be a literary classic, a book must be worthy of serious study.
If something is not worthy of serious study, then it is not a literary classic.
A
Any book worthy of serious study is a literary classic.
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 no literary classics.
B
A book is a literary classic only if it is worthy of serious study.
Must be true. As shown below, worthiness of serious study is also a necessary condition in order for a book to be a literary classic. 
C
There are no literary classics worthy of serious study.
Could be false. The stimulus only tells us that in order to be a literary classic, a book must be worthy of serious study. It is possible that there are no books that meet these requirements.
D
Some books worthy of serious study do not reveal anything significant about the human condition.
Could be false. It is possible that some books worthy of serious study do not reveal anything significant about the human condition. A necessary condition may occur without the sufficient condition occurring.
E
Some books that reveal something significant about the human condition are not literary classics.
Could be false. It is possible that some books that reveal something significant about the human condition are not literary classics. A necessary condition may occur without the sufficient condition occurring.