I believe the correct answer is:
Cause: Douglass witnesses the inhumane treatment of enslaved persons.
Effect: He becomes more aware of the brutality of slavery.
According to this excerpt from “Narrative of the Life of Frederick Douglass” written by Frederick Douglass, a former slave, the cause is Douglass directly witnessing the inhuman treatment of slaves, being one of them, which makes him more aware of the brutality of slavery. Douglass was lucky to live with a fine family before his mater died, and now that he is examined with other slaves and animals like they are the same he becomes more aware. But, the full effect of brutality is shown when Douglass hears that his grandmother won’t be bought and is, therefore, left in the woods.