Question

Choose the statement that best describes population density.

an increase in the number of people living in an area over time
a decrease in the number of people living in an area over time
the number of people who live in a square mile or kilometer
the number of live births per one thousand people in a year

Answer 1

The answer is: [C]:  
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           "the number of people who live in a square mile or kilometer" . 
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Let us examine the other answer choices:
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Answer choice: [A]: "an increase in the number of people living in an area over time" — refers to: "population growth".
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Answer choice: [B]: "a decrease in the number of people living in an area over time" — refers to: "population decline"; or, "depopulation".
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Answer choice [D]: "the number of live births per one thousand people in a year" — refers to: "birth rate". (as opposed to: "the number of deaths per one thousand in people in one year" — which refers to the "death rate"; or, "fatality rate").
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Answer 2

C. The number of people who live in a square mile or kilometer