Final answer:
The Vice President's formal responsibilities include presiding over the Senate as President of the Senate, casting tie-breaking votes, and being ready to assume the presidency if needed. The correct formal role is D. President of the Senate.
Step-by-step explanation:
The Vice President of the United States has two formal responsibilities as outlined in the Constitution. Primarily, the Vice President serves as the President of the Senate, a role that includes presiding over Senate sessions and casting tie-breaking votes when the Senate is evenly divided on a proposed bill or nomination. The Vice President's secondary constitutional role is to be ready to assume the presidency in the event of a vacancy or disability of the President. Beyond these formal duties, the Vice President can also accept additional responsibilities delegated by the President, which can significantly vary from administration to administration. These additional duties can range from largely ceremonial functions to wielding substantial influence in the governance of the country, depending on the President's discretion.
The correct answer to the student's question is D. President of the Senate. While the Vice President may also take on advisory roles or lead projects as assigned by the President, these are not formal responsibilities mandated by the Constitution.