Final answer:
The Grimké Sisters were unique in their abolitionist fight because they were Southern women who provided firsthand perspectives on slavery and were among the first to link the causes of abolition and women's rights. Therefore, the correct option C.
Step-by-step explanation:
What was unique about the Grimké Sisters' fight for abolition was c. They were from the South and had a unique perspective of slavery. Sarah and Angelina Grimké were born into a prominent slaveholding family in South Carolina, providing them with firsthand experience of the horrors of slavery. Upon converting to Quakerism, they moved North and joined the abolitionist movement.
Their Southern background allowed them to speak with authority on the ills of slavery, and their public lectures to mixed-gender audiences defied the norms of respectable society at the time. Further combining their abolitionist work with the struggle for female equality, they were pivotal in bringing attention to the dual issues of slavery and women's rights.