________to the man's timely coming, the________boy was saved. [ ]

A.Thanking; drown  

B.Thanks; drowned

C.Thanked; drowns  

D.Thanks; drowning

The rated operating time of a self-contained breathing device may be reduced in actual use because of（）.

A.pressure differences in the atmosphere

B.the length of the hose attached to the facepiece

C.the physical exertion of the person wearing the device

D.spaces containing poisonous vapors