Answer: The underlined phrase ("The true king") is A. an adjective phrase.
Step-by-step explanation: An adjective phrase is a group of words that modifies a noun or pronoun by describing it. Moreover, this type of phrase always contains an adjective which can appear at the beginning, at the middle or at the end of the phrase. "The true king" is an adjective phrase because it includes the adjective "true", which has been placed at the middle of the phrase. Furthermore, in this case, "true" is premodifying (and describing) the noun "king".