Final answer:
The adverb phrase in the sentence 'Walt scored fourteen points in twenty minutes' is 'in twenty minutes,' which modifies the verb 'scored' by indicating the time frame.
Step-by-step explanation:
The question concerns the identification of an adverb phrase in the given sentence, "Walt scored fourteen points in twenty minutes." An adverb phrase is a group of words that modifies, as a single unit, a verb, adjective, or adverb by providing additional details such as time, place, manner, or cause. In the provided sentence, the phrase 'in twenty minutes' modifies the verb 'scored' by specifying the time frame in which the action took place, thus functioning as an adverb phrase. The correct answer is a. in twenty minutes.