What is a political unit of different people or formerly independent state under the control of one ruler

a, both were musicians during the jazz age

i believe your answer is d)

during the 20th century, the role of the vice president has evolved into more of an executive branch position. now, the vice president is usually seen as an integral part of a president's administration and presides over the senate only on ceremonial occasions or when a tie-breaking vote may be needed.

protect u.s. businesses from competition