Final answer:
In the provided sentence, 'Sun' is a noun, which refers to the celestial body at the center of our solar system and serves as the subject of the sentence. The correct option is (A).
Step-by-step explanation:
In the sentence "The Sun is a burning ball of gas and gravity that keeps all the planets in the solar system," the word "Sun" functions as a noun. It serves as the subject of the sentence and is the name of the celestial body at the center of our solar system.
In this context, the Sun is being described with additional information, such as its composition and its gravitational role.
To identify the nouns, adjectives, verbs, and adverbs in any sentence, we should remember that these parts of speech can also appear in phrase forms, as explained in the provided reference materials.
In our original sentence, 'a burning ball of gas and gravity' is a noun phrase that provides more detail about the Sun. The verb in the sentence is 'is,' which links the subject (Sun) to the complement (burning ball of gas and gravity), and there are no adjectives or adverbs present.