Correct answer is (d) Carfentanil
Best explanation: Alfentanil, ultra-short acting analgesic. Sufentanil, a potent analgesic (5 to 10 times more potent than fentanyl) for use in heart surgery. Remifentanil has the benefit of rapid offset, even after prolonged infusions. Carfentanil has analgesic potency 10,000 times that of morphine and is used in veterinary practice to immobilize certain large animals such as elephants.