An example of covalent drug receptor interaction:: (A) Noradrenaline binding to β1  adrenergic receptor, (B) Acetylcholine binding to muscarinic receptor, (C) Prazosin binding to α1   adrenergic receptor, (D) Phenoxybenzamine binding to alpha adrenergic receptor
Answer is D. Phenoxybenamine is an irreversible (covalent) antagonist at alpha receptors. All other drugs mentioned are reversibly interacting with their receptors.