Final answer:
The phrase 'An accomplished artist, Leonardo da Vinci was mesmerized by flight and drew many sketches of unconventional and surprisingly modern flying machines.' is an example of a phrase.
Step-by-step explanation:
The answer to the question is A. Phrase.
In the given context, the phrase 'An accomplished artist, Leonardo da Vinci was mesmerized by flight and drew many sketches of unconventional and surprisingly modern flying machines.' is functioning as a descriptive phrase that provides additional information about Leonardo da Vinci.
It is not a clause because it does not contain a subject and a verb that can stand alone as a complete sentence.