The underlined word <em>unique </em>is used as C. predicate adjective in the sentence.
A predicate adjective is the adjective following a copulating/linking verb.
The linking verb here is <em>is, </em>and the predicate adjective is therefore the adjective following it, which is <em>unique. </em>
The answer is When because an adverb is a word that modifies a verb, adjective, determiner, clause, preposition, or sentence. Adverbs typically express manner, place, time, frequency, degree, level of certainty, etc.
This is False because the town form of government began in New England colonies.