Which of the following is an example of opportunity cost?

i do not know if this question has options, but a main impact of the federal reserve act of 1913, which created the federal reserve bank, was the international use of the u.s. dollar, which soon became the world's leading currency - particularly during world war i, since many nations around the world asked the united states for money.

(b) britain had a much larger navy than the u.s.

(d) the u.s. had a small army compared to britain.