This question is unusual in that the Conclusion comes first, followed by the Evidence. That’s probably because it’s an LSAT question, but occasionally we see this on the GMAT as well. Set a timer for 2.5 min and give it a shot:

Archaeologist: The mosaics that were removed from Zeugma, the ancient city now flooded by the runoff from Turkey’s Birecik Dam, should have been left there. We had all the information about them that we needed to draw archaeological conclusions, and future archaeologists studying the site, who may not have access to our records, might be misled by their absence.

Which one of the following, if assumed, most helps to justify the reasoning in the archaeologist’s argument?

(A) The only considerations that bear upon the question of whether the mosaics should have been removed are archaeological.
(B) Archaeologists studying a site can tell whether or not that site had been flooded at some time.
(C) The materials used in the construction of a mosaic are readily apparent when the mosaic is examined in its original location.
(D) Archaeological sites from which artifacts have been removed rarely mislead archaeologists who later study the site.
(E) The removal of artifacts from archaeological sites rarely has any environmental impact.

—

Evidence: 
-we have all info on M for archaeology
-future A’s might not have access to our records & be confused is M are gone

Conclusion: 
-M should have been left in situ

Concept Shift: 
-Even though the Conclusion comes first, I still find the evidence doesn’t do a good job justifying WHY they should have been left, given that there’s run-off. It seems like run-off would be a BAD thing for these mosaics!

The author is saying we need to leave the mosaics for the future archaeologists to study in case they don’t have our records, so the author is clearly assuming the mosaics would still be there for the future archaeologists if we put them back/left them there.

I like the word “justify” in the question-stem here. It always makes me think, “which of the following makes the author seem less crazy?” 

If the idea of “now flooded by the runoff from Turkey’s Birecik Dam” is NOT going to be part of the scope of the correct answer, then why is this detail even included? It would seem so odd.

Prediction: Something that explains WHY they should have been left there, even with the run-off/flooding.

On to the answer choices:

(A) The only considerations that bear upon the question of whether the mosaics should have been removed are archaeological. (it’s sort of on topic, so we can keep…for now)
(B) Archaeologists studying a site can tell whether or not that site had been flooded at some time. (we don’t know how this relates to why they should have been left there)
(C) The materials used in the construction of a mosaic are readily apparent when the mosaic is examined in its original location. (how they were constructed is not part of the argument)
(D) Archaeological sites from which artifacts have been removed rarely mislead archaeologists who later study the site. (on track, let’s keep)
(E) The removal of artifacts from archaeological sites rarely has any environmental impact. (environmental impact is totally outside the scope)

Let’s focus on the only two that seem to be on track:

(A) The only considerations that bear upon the question of whether the mosaics should have been removed are archaeological.
(D) Archaeological sites from which artifacts have been removed rarely mislead archaeologists who later study the site.

Let’s negate each one:

(A) Archaeological considerations are NOT the ONLY point of consideration.
(D) Removing mosaics WOULD mislead archaeologists.

The negation of (D) seems to SUPPORT the conclusion, saying yeah, we shouldn’t have removed them! It basically reiterates the evidence.

With (A), it’s like saying, “there’s other things we should consider.” Well, if there are other points to consider other than archaeological ones, then it definitely hurts the conclusion since the entire conclusion’s evidence is based on archaeology. Perhaps those other considerations would have something to do with the flooding??

I’ll be honest, I don’t LOVE (A) as an answer to an Assumption question but the keyword “justify” sort of makes this one a bit like a Strengthen question.

Hopefully, we can see here that (A) is just miles ahead of the other answer choices.

Takeaway: We don’t need a “perfect” answer; we just need one that “beats” the other four!