Samples from a ceramic vase found at a tomb in Sicily prove that the

The vase was manufactured in Greece.
It was found in Sicily at a tomb which was made 2700 yrs ago.

Conclusion: There was trade between Sicily and Greece 2,700 years ago.

What are we assuming here? That the vase was not placed there in Sicily many years later by someone. What if 1000 years ago, a descendent of the Sicilian occupant placed that vase there? Perhaps there was no trade 2700 years ago between Sicily and Greece but it started 1500 years ago.

Hence (D) is an assumption.

(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.

Irrelevant. We are given that the vase was made in Greece. That is not under inspection at all.

(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.

Again irrelevant. Same logic as above.

(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.

We don't need ships capable of transporting large quantities. Trade could have been in the form of traders travelling etc.

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

Irrelevant.