Final answer:
The Postal Service and AMTRAK are examples of government corporations, which are federal agencies providing services that are partly influenced by market forces and fulfill a public service.
Step-by-step explanation:
The United States Postal Service and AMTRAK are examples of government corporations. Government corporations are agencies formed by the federal government to administer a quasi-business enterprise. They operate independently from political influence to some degree and provide services that are partly subject to market forces and partly fulfill a public service that the government wants to maintain. These corporations do not have stockholders, but instead have a board of directors and are managed to continue their operations rather than to distribute profits as dividends. Examples cited include the U.S. Postal Service, which was a cabinet department before becoming a government corporation, and Amtrak, the National Railroad Passenger Corporation.