Bob would have come to the airport to see us off, but he ______. [ ]

A. is ill

B. has been ill

C. was ill

D. will he ill

生产经营单位应当在有危险因素的生产经营场所和有关设施、设备上，设置（）。

A、管理制度

B、操作规程

C、安全标语

D、警示标志