The correct sentence is: Some authors prefer to write novels that challenge readers to follow many characters and a complicated plot.
A novel is a fictitious prose narrative that is usually long and complex and that presents a usually connected sequence of events that represent characters and action. That is why novels <em>challenge readers to follow many characters and a complicated plot. </em>
A, C, and D all have commas where they are NOT necessary, so they are sentences that are considered NOT to have proper punctuation. Thus, the answer is B.
