The sentence which contains an adverbial phrase is B. Gertrude listened to her best friend Lillian in an attentive manner. An adverb phrase, or an adverb clause is meant to modify verbs, adverbs and adjectives. Remember, that it also can include a subject and/or a verb. This part of a sentence can tell you where”, “how”, “why”, or “when.”. In this sentence we have the features of modifying 'how': Gertrude listened to her best friend Lillian (HOW?) - in an attentive manner.
