Passage Summary: The government checks car pollution once a year by measuring what comes out of the tailpipe while the car is parked and running.

Reasoning: The passage describes the current method of emission testing: annual inspections of idling vehicles measuring tailpipe exhaust.

Analysis: To show that this enforcement is ineffective, we need to find a disconnect between the test conditions and real-world driving. If cars behave differently when they are actually moving or under a load than they do when idling, the test is a poor representation of actual pollution levels. Look for an answer choice that introduces a variable—such as speed, engine temperature, or different types of pollutants—that the current 'idling-only' test fails to capture. We want to undermine the assumption that a stationary test accurately reflects a car's total environmental impact.