Fragen über die Beispielsätze mit, und die Definition und Benutzung von "Concerning"

A: I have sent you a letter concerning the issue we discussed earlier.

That student's grades are very concerning.

Its concerning to hear that he has started gambling again.

Concerning your sentences, I hope my example sentences help!!😊

A: concerning and regarding are formal words used in Business English, preferably in written Speech. About is more flexible and can be used for both oral and written Speech as well as formal and informal settings. For example:
To your boss "Sir, I would like to discuss with you the matter regarding my request for vacation in September"
To your colleague, "Mr. Smith, when is it a good time to talk about the vacation schedule?"
To your supervisor, "Miss Williams, could I talk with you for a moment? It concerns my presentation in our joint meeting and I have a few things to go over with you before the meeting starts"

A: If it's a response to a formal question then yes it's natural.