This was likely the worst blight in the history of Supreme Court decisions. So say many experts on the Supreme Court.
The Case would never have reached the Supreme Court if slaves were not allowed to sue in the lower courts. In addition, there were many cases that were dealt with the slavery issue. This one was just the most infamous. A is not right.
Dred Scott centered around C. It was declared that Dred Scott could not claim freedom just because he lived in a free state. So C is wrong.
D is also incorrect. The Supreme Court ruled that even if the state of residence declared Dred Scott a citizen, he was not according the Federal Constitution. In one ruling, the whole festering question of states' rights was boiling in a pot ready to overflow into troubled waters.
The whole mess resolved itself by stating that slaves belonged to their owners.