We want to WEAKEN a CRITICISM. First lets rephrase the criticism from the passage in our own words: "Looking at Roman copies of Greek statues to learn about Greek sculpture doesn't always work because the statues have updated features that aren't Greek." To weaken this criticism, we want to prove that looking at Roman copies of Greek statues is still a valuable way to learn about Greek sculpture - maybe there aren't many non-Greek updated features, or we can learn something about Greek sculpture from the updated features anyway?

A. All Roman copies of Greek statues share a number of important characteristics that are absent from original Roman sculpture.
If these copies have features that aren't present in the Roman style, these features must be in the Greek style. This means that even if some features are updated, we know that some are not and can learn from those. This works!

B. Most ancient statues were melted down for reusable metal.
This doesn't impact our argument - whether or not Greek and Roman statues are rare now, we still run into the issue that we can't trust Roman copies of Greek statues to be accurate. Eliminate.

C. All art historians focus on one particular region or nationality in their studies.
Like in B, whether or not the art historians are focused on more than just Greece doesn't impact whether or not they can learn about Greece from Roman statues. Even if the historians can learn something valuable about Rome from the Roman statues doesn't matter - we specifically want to know if they can learn about Greece. Eliminate.

D. Many art historians who study Roman art do not make conclusions about Greek art on the basis of their observations.
If anything, this strengthens the criticism - most art historians don't use Roman art to learn about Greek art, so why would we use Roman statues to learn about Greek statues? Eliminate.

E. even those Roman statues that are not based on Greek artwork are significantly different from other forms of ancient sculpture.
This may even strengthen the criticism - the Roman style is distinct from all other styles, so it is likely that they made many updates in their copies of Greek statues to make them fit in with their style. Eliminate.