Answer:
Daily waterings keep Sheila's plants healthy, and she watches <u><em>closely</em></u> 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: <em>daily, healthy, closely, early.</em> But only <em>closely</em> modifies the verb. The rest modifies nouns, so they are adjectives.