量值准确一致的前提是被计量的量值必须具有能与国家计量基准直至国际计量基准相联系的特性，也就是（）。

When starting CPR on a drowning victim，you should（）.

A.start chest compressions before the victim is removed from the water

B.drain water from the lungs before ventilating

C.begin mouth-to-mouth ventilations as soon as possible

D.do not tilt the head back since it may cause vomiting