We have warned you.

The correct answer is: You have been warned.

The other options are incorrect because they do not follow the rules of English grammar.

• Option A: “You have been warned” is the correct way to say this sentence. It is in the passive voice, which means that the focus is on the action (being warned) rather than the person doing the action (we).
• Option B: “We have you warned” is in the active voice, but it is not grammatically correct. The verb “to warn” takes a direct object, so the sentence should be “We have warned you.”
• Option C: “Warned you have been” is not a grammatically correct sentence. The verb “to warn” takes a direct object, so the sentence should be “You have been warned.”
• Option D: “Have you been warned” is the correct way to ask this question. It is in the interrogative form, which means that it is asking a question.

I hope this explanation is helpful!