I am not an instructor but let me try explaining why I choose E.
So, I identified this as a Strengthen with Sufficient premise question and the conclusion is the last sentence "One must therefore either abandon the opinion of this majority of commentators or reject Mather's definition of Baroque painting, which says that for any painting to be considered Baroque, it must display opulence, heroic sweep, and extravagance".
The phrase "must display opulence, heroic sweep, and extravagance" is an entirely new concept in the conclusion so I looked for an answer choice that addresses this new concept, which narrowed it down to D and E. I choose E (Opulence, heroic sweep, and extravagance are not present in Caravaggio's paintings) as the answer because if Caravaggio's paintings DID display opulence, heroic sweep, and extravagance, then the conclusion stating that "one must therefore either abandon the opinion of this majority of commentators or reject Mather's definition of Baroque painting..." will not hold.