The correct answer is B, since that diagram best explains a cause and effect relationship that has shaped U.S. politics. In fact, restrictions on who can receive public campaign funds have contributed to the persistence of the two-party system.
Public funding of political campaigns in the United States is quite limited, so candidates end up going to private financing. This, in turn, only finances those who have real chances of getting the positions in the voting, which ends up closing the question between Democrats and Republicans, strengthening the two-party system.
They have both a chancellor and a president, so a president would be head of the government.
