---In recent years,      problem of global warming had been very serious.

   ---That is right. People are facing     number of natural disasters now.

A．\; a

B．\ ;the

C．the; a

D．a ;a

以下情况中为险性事故的（）

A.挤道岔

B.调车脱轨

C.未经批准，应停列车在站通过

D.客车错开车门、运行途中开门或车未停稳开门产生紧急制动