The answer is A. Appositive phrase is basically describing or renaming the noun in either long or short combination of words. For example: the insect, a cockroach, is in my room. A cockroach is the appositive phrase.
Explanation: a participle is a word formed from a verb and used as an adjective or a noun. A participle phrase is a group of words consisting of a participle and its modifiers (direct objects, indirect objects, or complements). In the given sentence, the phrase in brackets (sol at the farm store) is an example of a participle phrase (the participle is "sold") that acts as an adjective that is modifying the noun "pie."
I honestly don't think there is anything positive about peer pressure, but maybe it could be positive if your peers are trying to make you do something good? Sorry, I'm not totally sure...