D interrogative that what I think
C seems like a concluding sentence about how sandwiches were made.
Olaudah Equiano wasn't put into fetters on the slave ship because of his extreme youth.
When he was made to board the ship, he was still very young so I guess the slavers took pity on him and let him go about the ship freely, without having to be confined. Equiano was a slave, however, he was freed at one point, and then he started supporting the movement to end slavery.
B. hints that tell a reader what is going to happen in a story :)