单项选择题
Class A fires are best extinguished by quenching or cooling with （）.
A.deprival of oxygen B.a water spray C.soda-acid D.foam
单项选择题 A fire starts when the following （） factors come together.
单项选择题 （） can be operated independently or locked together and operated as a twin-job cranes of double capacity.
单项选择题 Some cranes are mounted in pairs on a common platform which can be rotated through（）.
