What is carefully as an adverb?

"Carefully" is already an adverb. It modifies a verb, adjective, or another adverb, describing how something is done.

Here are some examples:

* Verb: He carefully opened the box. (Describes how he opened the box)

* Adjective: She was carefully dressed for the occasion. (Describes how she was dressed)

* Adverb: She spoke very carefully to avoid making a mistake. (Describes how carefully she spoke)