Connotation gives an additional or secondary meaning for one word or expression beyond its first meaning. In this case the option B. a selection or decision is wrong because it is the denotative meaning of “choice”.
The option C. an expensive object is wrong because the text is not talking about values or prices.
The option A. difficult to understand also is wrong because the motivation of he repeatedly read the text was his continuous interest and not his difficulties to understand it.
The correct option is D. of very good quality, because it expresses Frederick Douglass emotions and feelings regarding the document and what he gained with the reading of these speeches.