Answer: 3. Population
Step-by-step explanation:
The Electoral College is what decides who the president will be because the person that gets the most electoral votes( more than 270) will be President.
The votes in the Electoral College are awarded to each state based on the number of seats they have in Congress and considering that the number of Seats a state has in the House of Representatives is based on their population, the Electoral College is indirectly based on population.