Final answer:
The adverb in the sentence is 'slowly'.
Step-by-step explanation:
The adverb in the sentence is slowly. An adverb is a word that describes or modifies a verb, adjective, or another adverb. In this case, the adverb 'slowly' tells us how the baby crawled across the floor. It provides information about the manner in which the action is performed.
Learn more about Adverbs