Which one of the following conducts Senate meetings when the vice president is unavailable?

Representative pro tempore

Congress pro tempore

President pro tempore

Member pro tempore

Since the vice president may often have other duties, the Senate is expected to elect officers to conduct its meetings. For example, the president pro tempore conducts Senate meetings when the vice president is unavailable. Answer President Pro Tempore

In the event that the Vice-President is unavailable, there would be a President pro tempore.

It means that the next to highest to the position will preside to represent his absence. Same goes in the absence of a President, the next in line to represent him is the Vice President.