某三级医院常年床位使用率超过100%，在计算平均护理时数时，我们用各级患者护理时数的总和除以（）

A.该病房开放床位数

B.该病房实际在院患者总数

C.一级患者人数

D.该病房患者总人数

E.占用床位数

The reason ______ he was late again was that he was caught in traffic jam in the rush hour.[ ]

A. which        

B. in which

C. for which    

D. of which