How did Mao maintain control over China once he
became its leader?

treaties

explanation:

after the roman empire, the catholic church began to unify by taking on many duties of a government.

i also think it is c

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.