Daily waterings keep Sheila's plants healthy, and she watches closely for early signs of disease.
Which word functions as an adverb in the sentence?

Daily waterings keep Sheila's plants healthy, and she watches closely for early signs of disease.

Explanation:

Adverbs are a part of speech that modifies a verb, an adjective or another adverb. They tell us how, when, where or in what manner something happened. Adverbs usually end on -ly, but that is not the only suffix they can end on.

In the given sentence by looking at the form, we can find several adverbs: daily, healthy, closely, early. But only closely modifies the verb. The rest modifies nouns, so they are adjectives.