Final answer:
The United States Secret Service option (b) is the agency responsible for protecting the President of the United States and other federal dignitaries.
Step-by-step explanation:
The agency responsible for protecting the President of the United States and other federal dignitaries is the United States Secret Service. The Secret Service is a federal law enforcement agency under the Department of Homeland Security and was established in 1865.
Initially created to combat counterfeit currency, it has since taken on additional roles, including protective services. The Secret Service is now primarily known for its protective mission's safeguarding the President, Vice-President, their respective families, visiting heads of state, and major presidential candidates.
The FBI, or Federal Bureau of Investigation, is the chief federal law enforcement agency within the U.S. borders and its activities are subject to constitutional protections such as the Fourth Amendment. The CIA, or Central Intelligence Agency, collects and analyzes intelligence in foreign countries and does not have a protective function.
On the other hand, the ATF, or Bureau of Alcohol, Tobacco, Firearms, and Explosives, specializes in enforcing federal laws related to firearms, explosives, arson, and alcohol and tobacco trafficking.