When the price per square meter is high, real estate companies will build higher buildings, resulting more densely populated cities. When land is cheap, as in smaller cities and villages, people tend to build lower buildings and therefore cities will be less dense.
This statement that best explains the reason why cities are densely populated is, Cities offer a wealth of 'opportunities' for citizens including education, jobs, access and healthcare.
<u>EXPLANATION:</u>
A city is a place where large human settles, generally have the extensive system for the housing, transportation, sanitation, health, education, utilities and communication.
The large population density facilitates the different parties like people, organization, business and government to interact with each other for the benefit of different parties.
I'd guess b on this one. I don't know the definition of watershed, but the amazon is a pretty big expanse of water "stretching" a long way (albeit that water doesn't stretch).
