Answer:
Here's the answer to the best of my ability..
You're asking for what sentence is missing a hyphen and I see nothing wrong with the one sentence that doesn't have a hyphen.
But if you're asking for what sentence is using a hyphen incorrectly then option B is your answer because machine gun doesn't need a hyphen.
If you're asking which sentences are using the hyphen correctly then option's A, and C are your answer.
If you're the question you asked has no mistakes then the best answer would be option D because that's the only option without a hyphen.
Hope this helps.
Sitting, A gerund phrase is a verbal ending in -ing that functions as a noun.
