Which answer choice best explains how the bolded participial phrase is used in this sentence?

Thinking it was after eight o'clock, Sam hurried home.


A It is used as a verb to name the main action of the sentence.


B It is used as an adverb to describe the verb hurried.


C It is used as a noun and acts as the subject of the sentence.


D It is used as an adjective to describe the noun Sam.