This line is not talking about his morals, or interests in general. So, from the given answers C and D are off the list from the possible answer. Now, because it says " not unacquainted", it is leaning toward the fact that he had basic or any kind of knowledge beforehand. So, the right answer indeed is A.
I believe you mixed the question with these answers, because the word broached doesn't refer to any of these answers - first of all, it is a verb, and all of the options are nouns. The meaning of this verb is <span>made a way into.</span>
