— How could they keep us waiting for so long?

— They got on the bus half an hour ago and they ________ be here in ten minutes, I think.

A．might

B．would

C．should

D．must

化学性窒息性气体中毒后皮肤、黏膜呈樱桃红色的原因主要是（）

A.耗氧量增加

B.静脉血氧含量下降

C.动脉血氧含量增加

D.动静脉血氧差下降

E.心跳及血液循环加快