What does the upper panel of Figure 2 in Chapter 18 of the textbook indicate happened to change the trade balance after the 1970s?

A. U.S. national saving was too low so foreign capital had to flow into the country to fund investment

B. U.S. national saving was too high and had to flow to other countries to fund foreign investment

C. U.S. investment was much lower than foreign investment

D. Tariffs on exports and imports impeded international trade