Answer: A) Why is it in the "interest of humanity" to preserve the "cargo" of slaves?
Explanation: In the given passage we can see how the speaker or narrator is describing some of the responsibilities of the slavers, like making sure that the slaves were healthy and clean on the voyage, and to preserve the cargo, the narrator says that this is in the slavers' personal interests but also that is the interest of humanity. In the excerpt it isn't very clear what is the speaker's viewpoint, to identify it the best question to ask is Why is it in the "interest of humanity" to preserve the "cargo" of slaves?