The correct answer is A) Slavery might become legal everywhere.
The Dred Scott vs. Sandford case was an important Supreme Court case about the rights of slaves in American society. In this case, Dred Scott was a slave who was brought to live in the free territory of Illinois. After his master passed away, he sued for his freedom. He argued that since he lived in a free territory, he should be free.
However, the Supreme Court ruled that slaves are not citizens, therefor they do not have the right to file lawsuits against their owners. Along with this, it also ruled that slave owners could bring their slaves wherever they want. This is because slaves are considered property not people. This is why Northerners feared slavery being legal everywhere, as there was now nothing stopping slave owners from bringing their slaves to the North.