Chetangupta,
The first step with Critical Reasoning questions is always to read the question and determine what the question is really asking. In this case, the question is written in a purposefully confusing way:
"Which of the following, if true, would be LEAST likely to be used to dispute the Chief of Police's claims?"
As you read this and think about the major types of CR questions (strengthen, weaken, ID the underlying assumption, and draw a conclusion), you should notice this question is about weakening the argument. It's really asking you which answer choice weakens the conclusion the least. The conclusion is that prosecuting people for small crimes leads to decreased crime overall).
Once you rephrase this into an easier to comprehend question type, take a look at the answers:
A would weaken or be irrelevant to the Chief's claim...it says that this hasn't worked in other cities.
B would weaken the conclusion by providing an alternate explanation for decreased crime.
C - If this were true, the crime rate should have actually gone up, which would actually strengthen the argument.
D would weaken the conclusion by providing an alternate explanation for decreased crime.
E would weaken the conclusion by providing an alternate explanation for decreased crime.
The one that weakens the arguments the least is C, as C actually strengthens the argument.
Tough question!
Brett