assumption

IMO D because it presents the most plausible explanation for how the Vase got there. answer?

Many atimes in assumption question an ans which eliminates the possibility of a condition, which can weaken the conclusion is the assumption
This is a typical example of such assumption question
Here the conclusion is there was trade between Sicily and Greece 2,700 years ago.
a)it is out of scope type ans if the Sicilian potters did not produce work of the same level of quality as did Greek potters , then we can only say that there was a diff .
b)wekens
c)presence of ships doesn't prove that trade took place
d)eliminates the possibility of a condition, which can weaken the conclusion is the assumption...hence correct
e)irrelevant

Samples from a ceramic vase found at a tomb in Sicily prove that the vase was manufactured in Greece. Since the occupant of the tomb died during the reign of a Sicilian ruler who lived 2,700 years ago, the location of the vase indicates that there was trade between Sicily and Greece 2,700 years ago.
Which of the following is an assumption on which the argument depends?

(A) Sicilian potters who lived during the reign of the ruler did not produce work of the same level of quality as did Greek potters.
Incorrect : Sicilian potters is irrelevant to the scope of the argument.

(B) Sicilian clay that was used in the manufacture of pottery during the ruler's reign bore little resemblance to Greek clay used to manufacture pottery at that time.
Incorrect : Sicilian clay is irrelevant to the scope of the argument.

(C) At the time that the occupant of the tomb was alive, there were ships capable of transporting large quantities of manufactured goods between Sicily and Greece.
Incorrect : There could be other methods of transportation also.

(D) The vase that was found at the Sicilian tomb was not placed there many generations later by descendants of the occupant of the tomb.
Correct : If we negate this answer choice it seriously hurts the argument. Hence this is correct.

(E) The occupant of the tomb was not a member of the royal family to which the Sicilian ruler belonged
Incorrect : Sicilian royal family is irrelevant here.

Simply saying that a choice is irrelevant or doesn't cater to the issue at hand, is not a correct way of eliminating the answer choice. I remember in one of Ron's videos in Manhattan GMAT "Thursdays with Ron", Ron said that a strengthen/Weaken/Explain Situation(or Resolve Paradox)/Assumption can have additional information that is/are not present in the stimulus/argument.
In fact one of the characteristics of a correct answer is that it always brings new additional information, to satisfy the question stem.
Following is my attempt to arrive at the correct answer choice:
(A) This choice is contrary to what is provided in the argument. We need to take whatever information provided in the stimulus as true. The argument already says that "Ceramic vase found at a tomb in Sicily proves that the vase was manufactured in Greece". How the argument came to this fact, we don't know and neither it's useful for us to know. The fact is "Vase was manufactured in Greece". This choice on negation "Sicilian potters produce the same quality of work as Greek potters" simply goes against the premise. Hence it can't be an assumption. AN assumption needs to strengthen the bridge between premise and conclusion and not weaken it any case.
(B) Sicilian clay is not coming anywhere into picture from the premise to conclusion. So this is simply out of scope.
(C) Ships capable of transporting large quantities (Negation: or small quantities) still don't strengthen (Negation also doesn't weaken)the conclusion of the argument. Even small boats could also be used to transport the pots. So the argument still stands. We need to remember here that a correct GMAT answer would leave no room for unjustified assumptions or loopholes.
(D) Correct. This is pretty obvious to be the correct answer.
(E) Even if the occupant of the tomb was member of the family, still there could be a trade between the two nations. We see that even after negating it doesn't affect conclusion of the argument. So this is not the correct answer.

We see that simply because the new term "Sicilian Potters" in (A), "Sicilian clay" in (B), "Methods of transportation" in (C) or "Royal family" in (E) are there, it doesn't make these answer choices wrong. A new info must be there, otherwise it in now way can strengthen/weaken/ or be an assumption to the argument.

Lastly, I earnestly request members to please post solutions iff they are posting, and explain why do they think it's the correct answer. Simply saying that this is OA or that this choice is irrelevant is wasting your and other's time. People come to forum to seek better explanations, not just read the question again and get the OAs.

Thanks and Regards
Prashant