Final answer:
The underlined subject of the sentence is a noun phrase, 'The sky scraper that was built last year.' This phrase functions as the main subject of the sentence and is neither an adverb phrase, a prepositional phrase, nor a verb phrase.
Step-by-step explanation:
The underlined subject of the sentence 'The sky scraper that was built last year has the most extraordinary architecture' is 'The sky scraper that was built last year.' This part of the sentence is functioning as a noun phrase. It is not an adverb phrase, a prepositional phrase, or a verb phrase as these have different functions within a sentence. Adverb phrases modify verbs, adjectives, or other adverbs; prepositional phrases often function as adverbials or as nominal phrases; and verb phrases are the part of the sentence that contains the verb and any direct or indirect object, but not the subject.
To identify the nouns, adjectives, verbs, and adverbs in a sentence, one needs to examine the roles each word or group of words plays. Nouns are persons, places, things, or ideas, adjectives describe nouns or pronouns, verbs express action or state of being, and adverbs modify verbs, adjectives, or other adverbs. Phrases like noun phrases or prepositional phrases can add extra information and function as different parts of speech in the sentence.