Question

according to article i, section 3 of the constitution, each senator must be
an adult who is at least 25 years old.
a lifetime resident of washington, dc.
a registered voter in ones state.
a us citizen for at least nine years.

Explanation:

Article I, Section 3 of the U.S. Constitution sets the qualifications for U.S. senators: they must be at least 30 years old, a U.S. citizen for at least nine years, and an inhabitant of the state they represent at the time of election. The other options are incorrect: 25 is the age for House members, senators do not need to be DC residents, and being a registered voter is not a constitutional requirement.

Answer:

D. a US citizen for at least nine years.