How is a city legally defined in the u. s.?
a. a collection of densely populated neighborhoods
b. an urban cultural center
c. a densely populated area with natural geographic boundaries
d. an urban unit with clear boundaries and a degree of autonomy

The correct answer should be D. an urban unit with clear boundaries and a degree of autonomy

A has to be a town, even though the definitions of the two are almost the same. B is not it because a city can be an industrial center, not a cultural one. C is not it because natural geographic boundaries are not necessary.