The correct answer is D) the ratification of the 14th amendment.
The choice that significantly undermined the rights of the states is the ratification of the 14th amendment.
The 14th amendment was ratified in 1868. In opposition to the Dred Scott decision, the 14th Amendment granted citizenship to all the people born in the United States or naturalized in the US. The decision included slaves, that before the amendment were viewed as property, not individuals. The amendment significantly undermined the rights of the states because it states that "No state shall make or enforce any law which should abridge the privileges or immunities of citizens of the United State." The government wanted to prevent situations such as the ones made by the Southern states before and during the Civil War.