In the sentence, the subject is 'the skyscraper that was built last year', which is a noun phrase. The noun phrase describes what the sentence is about. Thus, the correct answer is that the underlined subject is a noun phrase. ;
The subject of the sentence is 'the skyscraper that was built last year', which is identified as a noun phrase. This means it functions to describe what the sentence is about. Therefore, the correct choice is option B, a noun phrase.
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