In the sentence we are analyzing here, there is a present participle, "troubling". A present participle is formed by adding -ing to a verb stem (interesting, caring, loving, etc.). Present and past participles can function as adjectives, modifying nouns or pronouns in a sentence. That is precisely the case here, where "troubling" is modifying the noun "aspects", attributing a quality to it. For that reason, we can choose letter B as the best option.
Alternate and alternative are synonymous. Both words date to the middle of the 16th century, and both describe a choice apart from what is first offered: an alternate viewpoint; an alternative suggestion.
