A. opportunity cost
B. scale of preference
C. complementary demand
D. double of coincidence of wants

Correct Answer: Option D

D. double of coincidence of wants

Explanation

This occurs when two people have goods they are both happy to swap in exchange. i.e. a perfect barter exchange. a requirement that must be met before a trade can be made. It specifies that a trader must find another trader who is willing to trade what the first trader wants and at the same time wants what the first trader has.

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