Step 1: Understanding the Question:
The task is to identify the grammatical part of speech of the word "fluently" as it is used in the given sentence.
Step 2: Key Formula or Approach:
The approach is to analyze the function of the underlined word in the sentence. We need to determine what other word it is describing or modifying. Adverbs typically modify verbs, adjectives, or other adverbs, often answering questions like "how?", "when?", or "where?".
Step 3: Detailed Explanation:
In the sentence "She speaks fluently...", the word "fluently" describes how she speaks.
The word it modifies is "speaks", which is a verb (an action word).
A word that modifies a verb is an adverb.
Therefore, "fluently" is an adverb.
Step 4: Final Answer:
Since "fluently" describes the manner of the action (verb) "speaks", it is an adverb. Option (D) is the correct answer.