阅读短文，回答问题：What makes the museums' decisi…

阅读短文，回答问题：What makes the museums' decisions difficult, according to the text?

Over the past decade, a growing number of museums have returned objects that were taken from other countries during periods of colonial rule. The decisions are rarely simple. Curators must trace how each item left its place of origin, a task that can take years when records were lost or deliberately vague. In one recent case, a museum spent four years examining shipping lists and letters before concluding that a set of carved doors had been removed without the owners' consent.