input: The following are multiple choice questions (with answers) about medical knowledge.   **Question:** A 65-year-old man with metastatic lung cancer has been experiencing severe, unremitting pain. He has required escalating doses of oral morphine, but is now having dose limiting side-effects. His pain management team recommends using a medication that can reduce his opioid need through interaction with the NMDA-receptor. Which of the following was the most likely recommended agent?   (A) Propofol   (B) Ketamine   (C) Fentanyl   (D) Midazolam
output: ['(B) Ketamine <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Propofol  (B) Ketamine  (C) Fentanyl  (D) Midazolam <> possible answers', '  A 65-year-old man with metastatic lung cancer has been experiencing severe, unremitting pain. He has required escalating doses of oral morphine, but is now having dose limiting side-effects. His pain management team recommends using a medication that can reduce his opioid need through interaction with the NMDA-receptor. Which of the following was the most likely recommended agent? <> context']