Final answer:
Disparity refers to a difference or inequality. Frederick Douglass is talking about the difference or inequality between himself and others when he speaks of the 'sad sense of disparity.' He means he does not share in the benefits of justice, liberty, and independence.
Step-by-step explanation:
Disparity refers to a difference or inequality between two or more things. In the given context, Frederick Douglass is talking about the difference or inequality between himself and the people he is addressing. He says that there is a sad sense of disparity between them, indicating that he does not share in the benefits of justice, liberty, and independence that others enjoy. Therefore, option a) is the correct answer.