The applicant must be either a ________ of the US or a __________.

The requirement for the applicant to be either a U.S. Citizen or a Registered alien aligns with legal and regulatory standards for security personnel in many jurisdictions. U.S. Citizens have the full rights and responsibilities of citizenship, which includes the ability to work in various capacities without restrictions. Registered aliens, often referred to as lawful permanent residents, are non-citizens who have been granted the right to stay in the U.S. indefinitely. This status allows them to work legally in the country.

Having both categories—U.S. Citizens and Registered aliens—ensures that individuals in security roles have a level of trust and legitimacy that is necessary for such positions, given the responsibilities often associated with security jobs. These roles may involve access to sensitive areas and information, where citizenship or permanent resident status can provide some level of assurance regarding the individual’s legal standing and reliability.

The other options may not meet the necessary legal standards or may imply a status that does not permit employment in security roles, which is why "U.S. Citizen or Registered alien" is the most accurate choice.