The red car travelled speedily along the narrow road. What is adverb here?

The adverb here is the word speedily.

Just like an adjective describes a noun, so an adverb describes a verb.

So, given that the verb here is 'travelled', then the adverb tells us 'how did the red car travel?' - and the answer to that is speedily - and thus that is the adverb in the sentence.

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