Summarize Argument
The author concludes that Moon colonies will almost certainly be built, which will relieve overcrowding on Earth. This is based on the fact that as the human population goes up and the space available for housing on Earth goes down, the economic incentive to make Moon colonies will grow.
Identify and Describe Flaw
The author assumes that if the economic incentive for Moon colonies grows, then Moon colonies will be built. This overlooks the possibility that Moon colonies might not be built, even if there’s a growing economic incentive to build them. Having an incentive to do something merely means that you have a reason to do it. Even if that reason becomes more compelling, that doesn’t guarantee you’ll take the action.
A
It takes for granted that the economic incentive to construct colonies on the Moon will grow sufficiently to cause such a costly project to be undertaken.
If the incentive does not grow enough to cause the Moon colonies to be built, then that shows we cannot conclude the colonies will be built simply based on the incentive. So, the author does have to assume what (A) describes in order for the premise to support the conclusion.
B
It takes for granted that the only way of relieving severe overcrowding on Earth is the construction of colonies on the Moon.
The author does not assume there are no other ways to relieve overcrowding on Earth. The author’s position is simply that Moon colonies will be among the methods used to relieve overcrowding, not that other methods won’t be tried.
C
It overlooks the possibility that colonies will be built on the Moon regardless of any economic incentive to construct such colonies to house some of the population.
The conclusion is that the colonies will be built, so agreeing that they’ll be built doesn’t hurt the argument. (C) could be correct if the conclusion were that the colonies will be built because of the incentive. But, the incentive part is in the premise, not the conclusion.
D
It overlooks the possibility that colonies on the Moon might themselves quickly become overcrowded.
This possibility doen’t undermine the argument, becaue the conclusion only concerns overcrowding on Earth. Even if the Moon becomes overcrowded, there would still be at least some relief from overcrowding on Earth due to the Moon colonies.
E
It takes for granted that none of the human population would prefer to live on the Moon unless Earth were seriously overcrowded.
The argument doesn’t assume anything about people’s preferences. There might be some people who prefer to live on the Moon right now, even when Earth isn’t overcrowded. That wouldn’t impact the relationship between an economic incentive and the building of the colonies.