The correct answer is D.
The Electoral College was created as a compromise between election of the President by a vote in Congress and election of the President by a popular vote of qualified citizens.
The Electoral College consists of 538 electors. A majority of 270 electoral votes is required to elect the President.
Each candidate running for President in each state has his own group of electors. They are usually chosen by the candidate's party. After the elections, the electors meet in their separate states where they cast their votes for the President and the Vice President on separate ballots.