Question

Critical Reasoning -- Strengthen Argument: 
"Cities with higher public-transport usage typically experience lower air pollution levels." 

Which of the following, if true, most strengthens the argument? 

1. Cars emit significantly more pollutants per passenger compared to public buses. 
2. Public transport systems are cheaper than personal vehicles. 
3. People prefer using their own vehicles for convenience.
4. Pollution levels vary with weather conditions.

Hint:

To strengthen an argument, choose the option that provides direct evidence supporting the causal link or reduces alternative explanations.

Answer 1

Step 1: Apply the negation test used to confirm a strengthener: if reversing an option would hurt the argument, that option was truly holding it up.

Step 2: Reverse option 1, suppose cars actually emit less per passenger than buses, or the same amount. Then shifting riders to buses would not explain any pollution drop, and the argument's claim would lose its support entirely.

Step 3: Since negating option 1 damages the argument, option 1 must be doing real work in the original direction, so it strengthens the claim.

Step 4: The other three options do not pass this test, negating “public transport is cheaper,” “people prefer their own cars,” or “pollution varies with weather” leaves the transport-pollution claim completely unaffected, since none of them ever touched the mechanism.

Strongest support: Option 1.