How did the Missouri compromise affect the spread of slavery?

A. It declared that congress could make a recommendation for admitting a state

B. It drew a line through western territories to determine future free and slave states

C. It created a balance between slave states in the south and free states in the west

D. It declared that the popular vote in each state would decide the question of slavery

B. It drew a line through western territories to determine future free and slave states

Explanation:

The Missouri Compromise was a compromise orchestrated by the Congress that organized which states were slave free and which states were not. The state of Missouri requested in 1819 to become a slave state, this caused unbalance in the union because there would be more states with slaves than without them. With the Compromise, Maine was considered a free state, balancing the Union again.

The Compromise also drew a line across Louisiana Territory, creating a boundary between free and slave regions.

B. It drew a line through western territories to determine future free and slave states

It drew the line at the 45th parallel