Final answer:
The Supreme Court ruled in the Dred Scott v. Sandford case that Black Americans could not be citizens of the United States.
Step-by-step explanation:
The correct answer is a) that Black Americans could not be citizens of the United States. The Dred Scott v. Sandford case, decided by the Supreme Court in 1857, held that Black Americans, whether enslaved or free, were not U.S. citizens and therefore could not sue in federal court. The ruling also declared that the Missouri Compromise of 1820, which prohibited slavery in certain territories, was unconstitutional.
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