Concept:Punctuation rules for adjectives: Do not put a comma between a descriptive adjective and a classifying adjective (like nationality).
Explanation:"Beautiful" is a descriptive adjective and "European" is a classifying adjective (origin).
They are not coordinate (equal), so no comma is needed between them.
Option A incorrectly places a comma after "European".
Option B incorrectly places a comma after "met".
Option D incorrectly places a comma after "European".
Only Option C has no unnecessary commas and is correct.
Answer:C. I met a beautiful European woman.