QUESTION TEXT: In 1893, an excavation led by Wilhelm Dörpfeld…
QUESTION TYPE: Necessary Assumption
CONCLUSION: Wilhelm Dörpfeld was wrong to think that the city he found was Troy.
REASONING: The Iliad mentioned Troy, and said it was under siege for ten years. The city Dörpfeld found couldn’t have survived a ten year siege.
ANALYSIS: This sounds like a good argument. So you have to ask “how could this be wrong?”.
It’s clear that the city couldn’t survive a ten year siege. So we can’t attack that. But why must the siege be 10 years? The only fact in the argument is that the Iliad said the siege was ten years. A literary work isn’t necessarily true history. The argument assumes that the war was actually as long as the Iliad said.
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- This would explain why Dörpfeld thought the city might be Troy. But it doesn’t prove the city actually was Troy. The real site of Troy could still have not have been found in 1893.
Negation: In 1893, there was one other city that could have been Troy. But for a variety of reasons scholars considered it incredibly unlikely. - Remember, negating involves making an answer slightly untrue. There’s little difference between “no location clues” and “one location clue”.
We might be able to figure out the location of Troy from other clues (e.g. landmarks, documents found in the city, etc.)
Negation: The Iliad provides a single, vague clue as to the location of Troy. - This supports the argument, but isn’t necessary. There may have been other, shorter sieges.
Negation: Dörpfeld’s team found evidence of a ten day siege unrelated to the Trojan war. - This weakens the argument by increasing the odds that the city is Troy. The argument is stronger if this is negated.
Negation: The city lacked features of Troy. - CORRECT. If this isn’t true, then the Iliad’s evidence is irrelevant. Even if there was a Trojan War, we wouldn’t know how long it was.
Negation: The Iliad got the war’s length wrong.

C’s reasoning doesn’t seem correct. The answer stated “Dorpfeld’s team found no evidence in the city they excavated that a siege had occurred there” Meaning, no siege ever occurred at this city.
This is a necessary assumption question, so you test if the answer is right by negating it. You could negate C to say: “They did find evidence of a siege, but not one as long as the ten year Iliad siege.”
That negation shows the answer is still irrelevant to the argument even if negated.
Note: This is an old comment but I wanted to clarify the point.