According to Article I, Section 3 of the Constitution, each senator must be

Article I, Section 3 requires a senator to be at least 30 years old, to have been a U.S. citizen for at least nine years, and to live in the state they represent. Therefore, the correct choice is “a US citizen for at least nine years.” The age of 25 in choice C is the minimum age for a member of the House of Representatives, not a senator.

AI-written and checked against the verified answer.