5. As part of the Dred Scott decision, Chief Justice Roger B. Taney argued in 1857 that Congress could not prohibit someone from taking slaves into a federal territory because slaves were not citizens of the United States. Federal territories could not rule against slavery. Slave trade was still allowed in every state. Slaves were property, and property was defended by law.

The Chief Justice (Roger) of Supreme court in the case of Dred Scott argued that slaves were not citizens of the United States.

The Case of Dred Scott v. Sandford was about a fight for Slave right to become a citizen of United State.

The details of the Case entails that "Dred Scott" was a Slave who resides in a free state where slavery was prohibited and was not entitled to freedom to become a Citizen.

Hence, the Chief Justice (Roger) of the Supreme court in the case of Dred Scott argued that slaves were not citizens of the United States.

Therefore, the correct answer is Option A.

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A. slaves were not citizens of the United States.

Explanation:

Dred Scott decision was a watershed decision ruled by the Supreme Court of the United States in 1857. A suit was filed in the court by Dred Scott demanding his freedom from slavery. He claimed that since his owner took him to free state Illinois from Missouri, and died there, Dred considered himself a free slave. But was brought back to slavery under Missouri Compromise Act. In 1857, the Chief Justice Roger B. Taney ruled that Dred Scott is a slave, and the term 'citizen' does not apply to slaves, therefore, none of the rights provided for citizens of the US apply to Dred Scott.

Therefore, the correct answer is option A.

a case involving the laws of a single state.