You might be tempted to pick this answer choice because it seems to address the most glaring flaw in the argument: that the argument doesn't even establish a correlation between TV and homicide rates. Even if this answer choice did establish such a correlation in a way relevant to the argument, we would still be left with an argument that argues for causation from correlation alone — but you would be right to think that this would at least be a contender for a strengthening answer choice.

Crucially, however, this answer choice doesn't even establish the correlation we're interested in. It establishes a correlation between violent TV programs and homicide rates in "some areas," but doesn't establish that the presence of television sets (the physical object) in urban vs. rural areas correlates with the specific spike in urban vs. rural homicide rates discussed in the stimulus, let alone show that the advent of TV was causally linked to that spike. So this doesn't strengthen the argument at all.

This strengthens the argument by providing a causal mechanism that links television sets to homicide rates. If violence on TV is in fact a cause of violence in society, and not the other way around, this would show how the advent of TV explains the rise in homicide rates beginning earlier in urban areas than in rural ones, since TV came to urban areas earlier than rural ones.

You might notice that this assumes that TV came to urban areas before 1958, when homicide rates went up in those areas, and likewise for rural areas. And you would be right — this answer choice doesn't fix what might seem to be the most obvious flaw in the argument. But it does strengthen one aspect of the argument regardless: it's possible to strengthen a flawed argument without making it bulletproof. So this is the answer choice we want.

This doesn't strengthen the argument. It doesn't address any of the flaws we identified: we still don't know if the advent of TV was earlier than the rise in homicide rates, let alone causally linked to those rates. Even if we assume the first fact, that the advent of TV was prior to the rise in homicide rates, this answer choice would seem to weaken the argument, not strengthen it, because it tells us the first few years of TV didn't have any violent TV shows that might have prompted the rise in homicide rates.

This is irrelevant. It doesn't address any of the flaws in the argument, which isn't about the age when people were exposed to television, but about the timeframe when TV was introduced to certain places. And this answer choice doesn't specify what "effect" it's talking about. So this is completely unrelated to the argument.

This is also irrelevant. The argument doesn't tell us anything about leisure time. To assume that the popularization of TV necessarily indicates an increase in leisure time, and therefore potentially explains a rise in violence, would be to make an assumption that goes beyond the stimulus.