businesses such as the United States Postal Service and the Tennessee Valley Authority are independent agencies known as

Independent agencies of the United States federal government are those agencies that exist outside of the federal executive branch.

The correct answer is: Government corporations.

These are agencies that charge the public for a specific service. Examples of government corporations include: the Tennessee Valley Authority (TVA), the United States Postal Service, and Amtrak. They differ from private corporations in that they do not have shareholders, but are owned by the government.