This strengthens the argument by addressing the assumption that world population and overcrowding are directly related. If overcrowding has been proportional to the size of world population in the past, it’s more likely that this will be true in the future.

This strengthens the conclusion by pointing out that war and crime have increased as world population has increased over the last 100 years. It thus strengthens the link between increased world population and increased aggressive behavior.

This does not strengthen the argument, because it points out that there are other factors apart from overcrowding that can contribute to aggressive behavior and war. It doesn’t help to solidify the links between increased world population, overcrowding, and war.

This strengthens the argument because it addresses the assumption that rush-hour traffic is an example of people being overcrowded. (D) supports the idea that people’s behavior in rush-hour traffic can be used to predict their behavior in overcrowded environments.

This strengthens the argument. Since most mammals are more aggressive as population density increases and humans are mammals, it’s more likely that humans will also become more aggressive as population density increases.