This asks for something that weakens a conclusion, so it's a Weaken question.
The city has imposed a curfew on teenagers to combat the rise in theft by adolescents. A councilman concludes that it won't help lower the value of property stolen, based on the evidence that the majority of thefts by adolescents happen during the daytime.
Notice the switch between what is discussed in the councilman's evidence and his conclusion: in the evidence he discusses the incidence of thefts, but then he draws a conclusion regarding the value of property stolen. Therefore, he assumes that the value of the goods stolen is correlated with the incidence of theft. However, if adolescents steal goods of much greater value at night, then the curfew would have an impact on the total value of the property stolen, and the argument would be weakened.
(E) points out that the value of goods stolen at night is much greater, so it's the correct answer.
(A) and (D) are irrelevant to the argument; the councilman does not discuss alarm systems or police response times.
If anything, (B) strengthens the councilman's argument against the curfew by further pointing out that the curfew would be unnecessary. Since this is a Weaken question, eliminate choice (B).
(C) is an irrelevant comparison; the relative costs of replacing stolen goods and security guards have nothing to do with a curfew.