The best word to fill in the blank is "unimpeded."
So the complete sentence would read: "The guests were startled when the stranger moved unimpeded among them."
- A. impetuosity - refers to acting quickly and without thought.
- B. unimpeded - means moving freely without hindrance or obstruction.
- C. emphatic - relates to expressing something forcibly and clearly.
- D. profuse - means abundant or in great quantity.
"Unimpeded" fits the context of the statement, suggesting that the stranger moved freely among the guests, which could be surprising or startling to them.