Final answer:
The Twelfth Amendment reformed the electoral process after the election of 1800 by separating the selection of the president and vice president into separate elections within the Electoral College.
Step-by-step explanation:
The correct answer is (a) The Twelfth Amendment. After the election of 1800, Congress and the states ratified the Twelfth Amendment in 1804. This amendment reformed the electoral process by separating the selection of the president and vice president into separate elections within the Electoral College. It was enacted to avoid the issue of a tied vote between running mates, as happened between Thomas Jefferson and Aaron Burr in the previous election.