Nobody knows ______ yesterday.

A．how the accident happens

B．how does the accident happen

C．how the accident happened

D．how did the accident happen

监理单位发布的停、复工令应当事先向业主报告，如在紧急情况下未能事先报告时，则应在（）h内向业主作出局面报告。

A.12

B.24

C.48

D.72