Question

the main, or central, idea of the passage is encouraging cities to become denser would likely result in increased public transit use in america. how does the detail in bold develop the main idea?

compared to europeans, americans are relatively infrequent users of public transit. in a recent report on transit systems in various u.s. cities, researchers from the university of minnesotas center for transportation studies attempted to address this issue. although underuse of public transportation is a complex problem with many contributing factors, the reports authors noted one significant factor: when cities limit how tall their buildings can be, they tend to end up with more of what urban planners call sprawl. sprawl is the uncontrolled expansion of a citys population away from an urban center into suburban areas. sprawl makes public transit impractical for many residents because they must travel long distances to and from many different points. the authors recommend that cities pass laws to encourage people and businesses to cluster together in centralized areas. the idea is that the resulting high-density areas will be easier to serve with public transit.

it questions the influence of sprawl on public transit use.
it introduces and defines the term sprawl.
it explains how sprawl discourages the use of public transit.

Explanation:

The bold detail describes that sprawl forces residents to travel long, scattered routes, which makes public transit impractical. This directly connects low-density sprawl to low public transit use, supporting the main idea that denser cities would boost transit use by showing the opposite problem. The first option is wrong because it does not question sprawl's influence, it states it. The second is wrong because the term was defined earlier; the bold text focuses on its impact, not definition.

Answer:

It explains how sprawl discourages the use of public transit.