I voted B above thinking only in terms of illegally obtained goods.
Our art museum, the Wadsworth Atheneum, had a large Italian painting of Bathsheba in Her Bath (by Zucchi, I think). It was purchased in good faith. The Italian government claimed it had been looted by the Nazis. After some checking, it turned out their claim was valid. It was returned in exchange for a temporary loan of several Caravaggios for an exhibition. The situation was win-win. Good will on both sides.
Yale University has (in its Peabody Museum, I believe) some Peruvian artifacts that Peru claims were stolen. Nothing has yet been resolved. If they were stolen, this is the kind of merchandise that should be returned. If not, then no return. I think the more artifacts shared around the world, the better. Many more of us could travel to New Haven than to Lima --- no passport needed. Besides, I'm only an hour away from NH.
Museums are great places to tour the world and time-travel. More people should take advantage. That goes for libraries, too. The internet still can't match the visual impact in a museum or the feel of a book.