Question

Economists use changes in GDP to measure

the balance of trade with other countries.
any economic growth or shrinkage.
the causes of unemployment.
the distances between cities.

Answer 1

GDP = the total value of a country's output in goods/services/etc.

with that being said, are there any that stand out to you as possible candidates for the answer or possible candidates for elimination? for example, "distances between cities" is probably not the answer because GDP says nothing about distance