Can be useful in analyzing how a choice affects a particular market and shapes the economic system as a whole.
a. opportunity cost
b. marginal analysis
c. microeconomics
d. normative economics

A. Opportunity Cost

Explanation:

Choice affecting an economic system, market can be studied by : Macro Economics which studies Economy as 'a whole'.

On contrary, Microeconomics studies individual units of economy & marginal analysis is a tool used frequently in it. And ,Normative Economics reflects subjective non verifiable statements about how economy 'should be'.

So , all of three are not apt to analyse the above statement.

However, Opportunity Cost reflects cost of next best alternative sacrifised while making an economic choice. So ,it is useful to analyse 'choice' affecting an economic system, market. Eg :Opportunity cost is an important tool used in determining comparative advantage of a country in producing a good based on its opportunity cost (other good sacrifised to produce it).

answer: b) the us is the leading importer but not the leading exporter.

extra info:

the u.s is the largest importer but it is not the largest exporter as china sits on the top of the table when it comes to leading exporters.

but u.s is not far from first,

they rank in 2nd globally as the worlds largest exporter.

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i think the answer is a. science center.