This is a strengthen with a sufficient premise question. We have two competing interests in the stimulus: the car owners' security and the people trying to sleep at night. If the alarms are turned off at night, then the neighborhood can sleep without disturbance, but the car owners' cars could be subject to theft. However, if the car alarms are kept active during the night, then the neighborhood is kept up all night by car alarms, but the cars are less likely to be stolen. The conclusion of the argument takes a side and says that car alarms should be turned off. the big assumption being made is which group's interest is more important. In the case of this argument, the author is assuming the people trying to sleep's interests are more important.
(B) says, "In most cases when a car alarm sounds at night, it is a false alarm."
(B) definitely strengthens the conclusion by telling us that these alarms are actually likely to wake people up for no legitimate reason. However, the problem with (B) is that it doesn't tell us that we need to turn them off, and it fails to justify the conclusion that the people sleeping's interests are more important than the car owners' interests, so we can get rid of this choice.
(C) says, "Allowing the residents of a crowded city neighborhood to sleep undisturbed is more important than preventing car theft."
(C) is great because it's a premise that allows the argument to choose between the two options and conclude that the alarms should be shut off. It gives us a premise that the interests of the people sleeping are more important than the interests of the car owners, so it's the correct answer choice.
Hope this helps. Let us know if you have any other questions!
