Correct Option: D

In the context of BOP and international monetary systems, the reserve asset is the currency or other store of value that is primarily used by nations for their foreign reserves. BOP imbalances tend to manifest as hoards of the reserve asset being amassed by surplus countries, with deficit countries building debts denominated in the reserve asset or at least depleting their supply. Under a gold standard, the reserve asset for all members of the standard is gold. In the Bretton Woods system, either gold or the U.S. dollar could serve as the reserve asset, though its smooth operation depended on countries apart from the US choosing to keep most of their holdings in dollars.