Passage Summary: John believes that while writing about many different topics isn't necessary for a writer to be great, being able to explore a single topic deeply is a strict requirement.

Reasoning: John asserts that diversity of subject matter is not a requirement for greatness, but he insists that a great writer must possess the ability to explore a theme with depth.

Analysis: Since this is a 'Must be True' question, we must find a statement that is logically required by John's specific claims. John establishes a necessary condition: if you are a great writer, you must be able to explore a theme deeply. Logically, this commits him to the contrapositive: if a writer lacks the ability to explore a theme deeply, they cannot be a great writer. Look for an answer that reflects this necessary relationship or the rejection of Muriel's 'variety' requirement.