单项选择题
A portable foam fire extinguisher is placed in operation by（）
A.turning it upside down B.pressing the foam lever C.squeezing the grip handle D.opening the hose valve
单项选择题 Before you begin administering artificial respiration, you should be sure the victim（）
单项选择题 If liquid freon should come in with your skin, you should （）
单项选择题 If the effective bearing area has been reduced , remedial action should be taken（）
