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

不同的原油，其硫元素的含量相差很大，从（）分之几到百分之几。

A.十

B.百

C.千

D.万