The correct answer to this is A) the Missouri compromise because in 1820 a dispute erupted over the extension of slavery in Missouri Territory. Clay helped settle this dispute by gaining Congressional approval for a plan called the "Missouri Compromise". It brought in Maine as a free state and Missouri as a slave state (thus maintaining the balance in the Senate, which had included 11 free and 11 slave states), and it forbade slavery north of 36° 30' (the northern boundary of Arkansas and the latitude line) except in Missouri.
Hope this helps :)
