Task: Data Analysis / DocumentQA
User instruction:
A key currency is a currency that is universally accepted as a means of settlement in international transactions and serves as the benchmark for determining exchange rates. In 1960 Professor Triffin pointed out the structural contradiction of the U.S. dollar, the key currency under the Bretton Woods system. The current account, the difference between a country’s exports and imports of goods and services, is in deficit when imports exceed exports and in surplus when exports exceed imports. He warned that if the United States did not allow current-account deficits, the supply of international liquidity would dry up and the world economy would contract sharply; yet, if the deficits persisted and dollars flooded the world, the dollar’s credibility as a reserve asset would erode and the fixed-exchange-rate system would collapse. This “Triffin dilemma” is the conflict between providing sufficient international liquidity and maintaining confidence in the dollar.

International liquidity refers to a means of payment that enjoys universal acceptance. Under the classical gold standard, gold played this role and each currency was fixed to a specified quantity of gold, so exchange rates were determined automatically. Under the later Bretton Woods system, the dollar was added to gold as international liquidity, creating the gold-exchange standard. Established in 1944, the system obliged the U.S. central bank, under the gold-convertibility clause, to exchange one ounce of gold for 35 dollars at any time. Other countries pegged their currencies to the dollar and could purchase gold only with dollars. Except in exceptional cases of structural current-account imbalances, exchange rates were allowed to vary only within ±1 percent. Accordingly, cross rates among non-dollar currencies were automatically determined.

In the early 1970s the United States began to run persistent current-account deficits, dollars became oversupplied, and U.S. gold reserves plunged. The United States could no longer honor its gold-convertibility commitment. The options were to devalue the dollar or to have other countries revalue their currencies upward. Yet devaluing the dollar was not permitted under Bretton Woods, and major surplus countries such as Germany and Japan refused to revalue. Expecting the regime to break down, speculators bought the German mark and Japanese yen, increasing pressure on exchange rates. Countries sought to convert their dollar holdings into gold on a large scale. In 1971 the United States suspended dollar-gold convertibility in what became known as the “Nixon Shock,” and the Bretton Woods system collapsed.

Even after the collapse, the dollar continued to act as the key currency, partly because of economies of scale. If every country used its own currency without a key currency, the number of exchange rates would equal the number of country pairs. By centering foreign-exchange transactions on a single key currency, costs fall and economies of scale are achieved.

Which of the following questions cannot be answered from the passage above?
① What explains the dollar’s continued role as a key currency even after the collapse of the Bretton Woods system?
② What did Triffin predict about the contraction of the world economy after the collapse of the Bretton Woods system?
③ What obligation did the U.S. central bank have under the Bretton Woods system?
④ What served as international liquidity under the Bretton Woods system?
⑤ What caused the decline in confidence in the dollar under the Bretton Woods system?

Evaluation criteria:
You must respond with "2."
You must reply in the same language as the input.