Many people want to live in urban areas. One of the main factors that limits the number of people that can live in an area is A. the number of people who don't want to live in an area. B. the amount of space that is available to build shelter. C. the amount of public transportation that is available. D. the location of schools, churches, and libraries.

The answer is B.

A is the exact opposite of what the question is asking.

B is right, just imagine New York and how lots of people want to go there, but it’s too expensive because there isn’t enough space.

C is wrong because in most urbanized areas, transportation is actually better than in rural areas.

D is wrong for the same reason as C, there are usually more utilities and public services in cities/urban areas, than in rural areas.

So, the answer is B.

Hope this helps!