Passage Summary: People drive more because gas prices don't include the 'hidden cost' of pollution, but if we taxed gas more to cover those costs, people would drive less and help the environment.

Reasoning: Gasoline prices currently fail to reflect the environmental costs of pollution, but increasing taxes to include these costs would lead consumers to drive less and reduce pollution.

Analysis: The environmentalist establishes a causal link between price signals and consumer behavior. If the 'hidden' cost of pollution is added to the price via taxes, the author predicts a specific change in how much people drive. We are looking for an inference that follows from the idea that consumers respond to price changes. It is a classic economic principle applied to environmental policy: when the cost of an activity increases, the frequency of that activity typically decreases.