No, it is not an adverb. Class is a noun, with several meanings. Class to mean "sophistication" has the adjective "classy" and the adverb form "classily."
Adverb
The adverb is late.
outside
This is my favorite class. This class is my favorite.
The adverb is late.
"Late" is the adverb in the sentence. It describes the action of the students arriving late to their English class.
Highly is the adverb.
The adverb form is liberally. He gave money liberally to all the students in the class.
no? because the adverb is doing in the class.
Loudly is a good adverb for speak, i.e. "In class, Isabelle tends to speak loudly"
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No, the compound word 'underwater' is an adjective or an adverb. Examples:Our botany class is studying underwater plants. (adjective)Our swimming class is learning to swim underwater. (adverb)