Answer:
A. He contrasts ideas to show his own sadness.
Step-by-step explanation:
The fourth of July is marked as the day of independence from British rule in America. The slave in the text noted that while that day marked independence for the Americans, it was not the same for him who still had to remain a slave.
A contrast, which is a difference between two things is therefore drawn between the condition of the slave and the Americans. It also shows the sadness of the slave in his condition.