Answer:
C. to cast tie-breaking votes in the Senate
Explanation:
In the 20th and 21th centuries the vicepresident's figure turned into a position more related to the executive branch, and is often considered a crucial constituent in the president's administration.
Apart from succeeding the president in those two cases, the only remaning constitutional duty of a vicepresident is to chair the Senate. A vice president is not able to vote in the Senate but for breaking a tie, and needs the permission of the senators to appeal to the Senate in a formal way.
