Answer:
c. A candidate must be born in the United States.
Explanation:
According to Article I, section 3 clause 3 of the Constitution of the United States, it is clearly stated that
"No Person shall be a Senator who shall not have attained to the Age of thirty Years, and been nine Years a Citizen of the United States, and who shall not, when elected, be an Inhabitant of that State for which he shall be chosen."
So, any candidate for a senator has to be a citizen of the country and must be at least more than 30 years of age. He must also be a resident of that place he wishes to represent, meaning he must be a legal resident of the state from which he wishes to be the Senator of. But there is no rule as such for him/her to be a born in the United States.
