The answer that is not true is A: "Scott could only sue in state courts."
Whether Dred Scott, as a slave, had any legal right to sue in court was a matter that applied whether talking about state or federal courts. When Scott's suit was rejected by a state of Missouri court, Scott and his supporters managed to bring the case into a federal court, and it went all the way to the Supreme Court. Though the Supreme Court at the time ruled that Scott had no right to bring the suit because he was a slave and not a citizen (point D above), the case gave Chief Justice Roger Taney opportunity to make further statements regarding the slavery issue, including points B and C in your list above.
The question is asking to determine what continent is not yet touched by the European explorers, and i would say that the answer would be that they explored every continent and the last one of them is Antartica. I hope you are satisfied with my answer and feel free to ask for more
