Passage Summary: Since thieves steal what rich collectors want to buy, museums should put extra guards on their most expensive pieces.

Conclusion: Museums should concentrate their security efforts on their most expensive and valuable items.

Reasoning: Art theft is increasing, and because thieves steal what their wealthy buyers want, they target the items those buyers find most desirable.

Analysis: There is a significant 'Gap' here between what is 'valuable' and what 'customers are most interested in buying.' The argument assumes that these two categories perfectly overlap. To find the necessary assumption, ask yourself: what if wealthy collectors actually prefer rare, less expensive artifacts over the most famous, high-priced masterpieces? If that were true, the museum's plan to guard only the 'most valuable' pieces would leave the actual targets unprotected.