Answer:
Among the options given on the question, the answer is option D.
a US citizen for at least nine years.
Explanation: Article one has described the legislative branch of the Federal government which is the United States Congress. Under the sections of this article the rules of the congress is consist of House of representatives and the senates. The qualification of the senator is described under the section 3. The qualification for a US senators are given below.
1. One who wants to be an senator must be at least 30 years old.
2. He/She need to be the citizen of United States for at least 9 years.
3. He/She need to be the resident of the area from which he is elected.
So the answer of the question is a US senator must be the citizen of the US for at least 9 years.
