When the author says that the success of the gold-exchange standard "depended on the superior position of the United States in world trade" (paragraph 4), she is most probably referring to the idea that

A．under this system, the United States was required to lend money to any computer that asked.
B．under this system, the United States was the only country allowed to maintain gold reserves.
C．tying the value of most currencies to any one currency requires that that currency be stable.
D．the gold-exchange standard is less flexible in meeting currency demands than the gold standard.