Hi there! I think I can help here.

nfr007
Violent crime in this town is a becoming a serious problem. Compared to last year, local law enforcement agencies
have responded to 17 percent more calls involving violent crimes, showing that the average citizen of this town is
more likely than ever to become a victim of a violent crime.
Which one of the following, if true, most seriously weakens the argument?
E. Community officials have shown that a relatively small number of repeat offenders commit the majority of violent crimes in the town.
Why is the answer not E ?
First let's take a look at the argument and identify the conclusion and premises.
Conclusion: average person more likely to be a victim of violent crime
Premise: police responded to 17% more calls related to violent crime
Now we have to find a reason to doubt the conclusion. We need to think about why the average person is NOT at risk of a violent crime. One thing that stands out is that we are given a percent and have not idea what the actually values are, like the towns population and violent crimes this year and last year. But I am straying from your question.
Why is it not E? Well, E does takes some steps towards weakening the argument since we are told about the people who commit the crimes, but ultimately, it does not provide any evidence for why people in the town might be safe from violent crime. Answer choice E only tells us about the people commit the crimes—not why crimes might not happen to the average citizen.
On the other hand, answer choice C provides a reason for why there has been an increase in reported crimes, but not necessarily an increase in crime. This provides evidence that people are not less safe now, but that people are reporting these crimes more.
Does this make sense?
I hope it helps!