What entity does the MPS operate as an extension of?

The MPS, or Mail Processing System, operates as an extension of the United States Postal Service (USPS). This is because the MPS is designed to enhance the efficiency and effectiveness of mail processing and distribution under the umbrella of the USPS, which is responsible for providing postal services across the United States. The focus is on ensuring that mail is processed promptly and accurately, which is vital for the USPS to fulfill its mission of reliable mail delivery.

The other entities listed, such as the Federal Aviation Administration, Department of Defense, and Federal Bureau of Investigation, operate in different sectors and do not have a direct relationship or function concerning the postal services and mail processing systems. Each of these organizations has distinct roles that do not intersect with the operations and mandates of the USPS. Thus, the MPS is specifically aligned with the USPS, making it the correct answer.