Passage Summary: Houses changed after the war because air-conditioning became cheap, making old-fashioned ways of staying cool, like high ceilings, unnecessary for sales.

Conclusion: The availability and low cost of air-conditioning were the primary causes of specific architectural changes in North American homes after World War II.

Reasoning: After the war, builders noticed that houses without traditional cooling features like high ceilings and thick walls sold well if they were equipped with air-conditioning.

Analysis: The author is making a causal claim: AC availability caused the shift away from high ceilings and thick walls. To weaken this, we need to find an alternative explanation for why those architectural features disappeared. If builders switched to lower ceilings for reasons unrelated to AC—such as a shortage of building materials or a change in aesthetic fashion—the link between AC and architecture is severed. Look for an answer choice that provides a different reason for the change in home design.