Passage Summary: After the speed limit was lowered, there were fewer bad car crashes, so the new limit must be the reason for the safety improvement.

Conclusion: The reduction in the speed limit was the cause of the decrease in serious traffic accidents.

Reasoning: Serious accidents dropped by 35 percent during the same five-year period that followed the lowering of the speed limit.

Analysis: This argument falls into the classic trap of assuming that because two things happened at the same time, one caused the other. To weaken this, we need to find an alternative explanation for why accidents decreased between 1986 and 1990. Perhaps car manufacturers introduced airbags during those years, or a new highway was built that diverted dangerous traffic away from Park Road. Look for an answer that introduces a 'third variable' that could account for the improved safety record.