Answer:
A) Many Southerners feared more Northerners would try to weaken slavery through revolts or through the national government, so they seceded.
Step-by-step explanation:
The most pressing political question by the late 1850s in the US was the slavery.
The Northerners wanted the Southerns to abolish the slavery, which the Southerns did not want. This led to some sourthern states to withdraw from the union(seceed), which led to the Civil War.
So the correct answer is:
A) Many Southerners feared more Northerners would try to weaken slavery through revolts or through the national government, so they seceded.