Final answer:
A national currency was adopted with the creation of Federal Reserve Notes in b.1913 with the establishment of the Federal Reserve Act. This Act created the modern central banking system and gave the Federal Reserve the authority to issue new paper currency.
Step-by-step explanation:
The national currency was adopted with the creation of the Federal Reserve Notes due to the establishment of the Federal Reserve Act of 1913. This Act was significant because it created the modern central banking system in the United States, which included the authority to issue new paper currency in times of emergency and was essential in regulating the nation's money supply and credit. The Federal Reserve System, as structured by the Act, was divided into twelve districts, each affiliated with a decentralized private banking system controlled by the federal government, and by 1923, it encompassed approximately 70% of the nation's banking resources. Therefore, the correct answer to the question is b. 1913.