Which of the following is an adverb?

An adverb is a part of speech that typically modifies a verb, an adjective, or another adverb, often conveying information about how, when, where, or to what extent something occurs. "Quickly" serves as an adverb because it describes the manner in which an action is performed, answering the question "how?" For example, in the sentence "She runs quickly," the adverb modifies the verb "runs," indicating the speed or manner of the running.

In contrast, the other choices do not function as adverbs. "Blue" is an adjective that describes a noun by providing information about color. "Happy" is also an adjective, used to express a state or condition related to a noun, such as in "She is happy." "Table" is a noun that identifies a physical object. Understanding the role of these parts of speech helps to recognize why "quickly" is the only option that correctly fits the definition of an adverb.