这个标志是何含义？（）
A．横过道路设施
B．应急避难场所
C．生活服务区
D．行人专用通道
参考答案：B
临界胶团浓度
Forty percent of the rats included in an experiment were male rats. If some of the rats died during the experiment and 30 percent of the rats that died were male rats, what was the ratio of the death rate among the male rats to the death rate among the female rats ？（）
A.A
B.B
C.C
D.D
E.E
