Answer:
C. president pro tempore
Explanation:
The president pro tempore of the United States Senate is the second most important position in the Senate and the highest position as senator. It is established by the First Article of the Constitution of the United States. The Vice President of the United States is the President of the ex officio Senate, this being the highest position of a member of the Senate; during his absence, the President pro tempore chairs the Senate. The President pro tempore is elected by the Senate; by custom it is, typically, the Senior Senator of the Party with majority in the Senate. Normally, neither the Vice President of the United States nor the President pro tempore preside; instead, this position is generally delegated to another party senator with a majority in the Senate. The President pro tempore is the third person in succession to President of the United States, after the Vice President of the United States and the President of the House of Representatives of the United States.
