Final answer:
The underlined subject of this sentence is a noun phrase
Step-by-step explanation:
The underlined subject of this sentence is a noun phrase. A noun phrase is a group of words that functions as a noun in a sentence. In this sentence, the noun phrase "The skyscraper that was built last year" is the subject because it is the main focus of the sentence and performs the action of having extraordinary architecture.
Learn more about subject of the sentence