Read the excerpt below and answer the question. I have no accurate knowledge of my age, never having seen any authentic record containing it. By far the larger part of the slaves know as little of their ages as horses know of theirs, and it is the wish of most masters within my knowledge to keep their slaves ignorant.

Why does Douglass compare slaves to horses in this excerpt from Narrative of the Life of Frederick Douglass, An American Slave?

to show how poorly kept records were in those days
to show how naive he was at that age
to show how hard slaves had to work
to show how dehumanizing slavery was