What is a branch of the United States Postal Service that serves military personnel under the jurisdiction of postmasters in cities like New York or San Francisco?

The correct choice is Military Post Offices (MPOs). Military Post Offices play a critical role in providing postal services to military personnel, ensuring they have access to mail just like civilians in the general population. These facilities operate under the jurisdiction of postmasters in major cities, which streamlines mail delivery and helps maintain connections between service members and their families.

MPOs offer services that accommodate the unique needs of military personnel, including the forwarding of mail to deployed locations and ensuring secure and reliable postal delivery in various settings. This makes them a vital component of the military's communication infrastructure.

Other options, while related to postal services, do not specifically focus on the function and jurisdiction of serving military personnel like MPOs do. For example, a Military Mail Terminal handles larger volumes of military mail but does not directly serve military personnel in the same operational capacity. Understanding the specific roles and responsibilities of these postal entities helps clarify the importance of Military Post Offices in supporting those who serve.