呼吸性酸中毒合并代谢性碱中毒的血气改变有（）
A.pH下降
B.HCO3-减少
C.血钾降低
D.血氯降低
E.二氧化碳分压下降
参考答案：C, D
There are many kinds of synthetic materials, ______ plastics are the most common.
A．between which
B．of which
C．in which
D．among which
自然引风式扩散燃烧有（）个特点。
A.四
B.五
C.六
D.七
