When using carbon dioxide to fight a fire on a bulkhead，the CO₂ should be applied（）.

A.first to the bottom of the flaming area，sweeping from side to side，and following the flames upward

B.in a circular motion from the middle of the bulkhead outward

C.to the top of the flaming area，sweeping from side to side，and working toward the bottom

D.in an up-and-down motion from one side of the bulkhead to the other

质反应的特点有（）

A.频数分布曲线为正态分布曲线

B.无法计算出ED50

C.用全或无、阳性或阴性表示

D.可用死亡与生存、惊厥与不惊厥表示