Answer:
C) The U.S.dollar became a vehicle currency after World War II when all of the world's major currencies were tied indirectly to the dollar because it was the most stable currency.
Explanation:
The simple fact that 60% of all US currency is held by non-US citizens or residents, and the fact that the US economy is the largest in the world, gives us an idea that the world used the US dollar as the global currency. Even when the purchasing power parity is calculated to level off differences in prices between nations, the US currency is the base currency. Even before WWII, the US dollar and the British pound were the most important currencies in the world, but after the was, only the dollar remained as the world's preferred currency.
A vehicle currency is a currency used in international transactions (trade and other financial transactions) even if no country involved in the transaction had the US dollar as its official currency, e.g. American companies cannot consider the US dollar a vehicle currency because it is their own domestic currency.
For a while the euro, the yen, and now the yuan, are trying to become vehicle currencies, but they are still far away form reaching the same status as the US dollar. E.g. due to the recent world crisis, all currencies have depreciated against the US dollar because everyone is desperate to purchase dollars, even foreign governments.