Which of the Following Statements Is True

Which of the following statements is true?

A) The euro is the common currency of the countries in the European Union.
B) Once a common currency was introduced, countries in the European Union all wanted to follow the same monetary and fiscal policies.
C) One factor contributing to the success of a common currency in Europe is that, generally, the various countries face the same economic problems at the same time.
D) All of the above.