Which of the Following Was the Rationale Behind the Missouri

Which of the following was the rationale behind the Missouri Compromise of 1820, which matched Missouri's entry into the Union as a slave state with Maine's entry into the Union as a free state?

A) The parties compromised so the balance in the executive's cabinet between free and slave states would be maintained.
B) The parties compromised so the balance in the House of Representatives between free and slave states would be maintained.
C) The parties compromised so the balance in the Senate between free and slave states would be maintained.
D) The parties compromised so the balance on the Supreme Court between free and slave states would be maintained.