Answer: A) mighty, unabated.
Explanation: an adjective is a word that describes or modify a noun. From the given options, the choice that best represents the use of strong adjective in the given paragraph from Narrative of the Life of Frederick Douglass, is the corresponding to option A: the adjective "mighty" modifies the noun "speeches" ("I met with one of Sheridan's mighty speeches") and the adjective "unabated" modifies the noun "interest" ("I read them over and over again with unabated interest").