But for your timely warning, we have been unaware of the danger. Thank you very much! A. s

网友回答

A. shall
B. must
C. will
(答案→)D. would
解析：句意：要不是你及时提醒，我们就不会意识到危险。非常感谢您！此处but for意为：要不是。
表示与过去的事实相反，主句用would+have done的形式。故选D。