Passage Summary: A city official argues that studded tires cause road damage, not big trucks, because other places with lots of trucks only get these ruts if they also use those specific tires.

Conclusion: Studded snow tires, rather than large trucks, are the primary cause of road ruts in the city.

Reasoning: Other regions with similar truck traffic and snowfall only experience comparable road ruts if they also permit the use of studded snow tires.

Analysis: The official uses a 'method of difference' to isolate the cause, but the argument assumes that the cities being compared are similar in all other relevant ways. To strengthen this, look for an answer that rules out other potential differences, such as the quality of road materials or specific weather patterns. If we can confirm that the ruts specifically match the physical pattern of studded tire use, the conclusion becomes much more robust. Strengthening a causal argument often involves closing the door on alternative explanations.