单选题 — I'm sorry I stepped outside for a smoke. I was very tired.
— There is no ______ for this while you are on duty.
  • A.reason
  • B.excuse
  • C.cause
  • D.explanation
【正确答案】 B
【答案解析】[解析] reason意为“原因，理由”，excuse意为“借口”，cause意为“起因，原因”，explanation意为“解释”。根据语境可知，B为最佳选项。