发泡倍数是指（）与形成该泡沫的泡沫混合液体积的比值。
参考答案：泡沫体积
质坚实，断面白色或淡黄色，富粉性，横切面可见略呈放射状排列的黄色木质部小孔的是（）
A．野葛
B．甘葛藤
C．密花豆
D．天花粉
E．山豆根
Most of George Bernard Shaw's plays are concerned with political, economic, moral, or religious problems, and thus, can be termed as ______ plays.
A. comic B. tragicC. problem D. realistic
