The correct answer is D) Senators may speak for as long as they like and on any subject they choose.
A difference between the rules for debate in the Senate and those in the House is "Senators may speak for as long as they like and on any subject they choose."
When Senators are debating, the presiding officer monitors the session says who speaks. They correctly address the presiding officerñ. Senators have minimum regulations but only can not make more than two interventions in motion during the same day. The number of Senators in the US Senate is 100.