Which best explains how the Mongols under Genghis Khan were able to establish and maintain a large empire?

In presidential elections if no candidate receives a majority of the election votes, a. the winner is decided by the house of representative’s. b. the current president remains in office for four more years. c. the winner is decided by the senate. d. a runoff election is held in december between the two candidates who received the most votes in the general election.