Overcrowding inclines human beings toward aggressive, competitive behavior.
Conclusion (this shows that)
As the world population grows, aggressive behaviors will increase, including more war and crime.
Intermediate Conclusion
Overcrowding inclines humans toward aggressive behavior.
Evidence
People are usually considerate, but become jerks during rush-hour traffic or at crowded sporting events.
Evaluate
There is a new term in the conclusion (world population growth) and a repeated term (aggression, which is discussed in the evidence).
What is the author assuming happens as the world population grows?
She must think there will be more overcrowding. After all, more people on the same globe does sound like higher density. But will it necessarily create overcrowding?
If we were trying to weaken this argument, we might say
We might also argue that there will be technological innovations that will somehow alleviate aggression, or make things like war / crime less likely.
So if we're strengthening the argument, we would counter those objections. We would want to believe that more population DOES mean overcrowding, and that new technologies will NOT alleviate these problems.
Goal
Eliminate the four answers that help tell the story that more people on Earth will lead to more overcrowding, which will lead to more aggression / war / crime.