While this answer choice strengthens the evidence, it fails to support the relationship between the premise and conclusion (i.e., the argument). The author makes a jump from a premise about an assignment to a conclusion about books—this doesn’t fill that gap.

This strengthens the argument by substantiating the author’s assumption that students will print out books in addition to assignments. (B) says after a certain length people will print the reading material, strengthening the relationship between the premise and conclusion.

This does not affect the argument. The word “some” could mean just one or two people—one person having vision issues due to computer screens doesn’t affect our argument at all.

This does not affect the argument. While it may be true that online books would be full of errors if they are not carefully read through, there is no reason for us to believe that they aren’t carefully read through every time.

This does not affect the argument. The relative popularity between books on cassette tape and their printed version tells us nothing about the relationship between books delivered via computer and their printed versions.