Which sentence contains an adverb?

AThree brown-and-white birds chirped.incorrect answer
BThe gymnast's routine was perfectly executed.incorrect answer
CA sluggish Tim stumbled to the bus stop.incorrect answer
DTim had trouble answering the difficult question.incorrect answer

The correct answer is C: "A sluggish Tim stumbled to the bus stop." The word "sluggish" is an adverb describing how Tim stumbled.