Passage Summary: Two people are debating how to regulate pollution; one wants to use long-term averages, while the other argues that averages are misleading—like calculating a car's speed by including the time it spends stopped at red lights.

Reasoning: Levin uses an analogy of speed limits to argue that measuring average emissions is dangerous because it ignores harmful short-term peaks.

Analysis: In Levin's analogy, the 'peak speed' represents the dangerous high-emission periods he wants to regulate. The 'average speed' represents the regulatory method Shaw is proposing. Therefore, the time a vehicle spends at a 'stoplight' represents a period of low or zero activity that artificially lowers the average. Look for an answer that describes a power plant operating at low capacity or being temporarily shut down, as this is what would 'dilute' the average emission levels in the same way a red light dilutes average driving speed.