弗里德赖希（Friedreich）共济失调发病年龄为（）
A.40岁左右
B.5岁以下
C.5～15岁
D.40岁以后
E.20～40岁
参考答案：C
闪点越高的物质，火灾危险性越小。（）
In a certain group of people,
of the people are men, and
of the men have brown eyes. If
of the people have brown eyes, then what fraction of the group are women who do not have brown eyes
of the people are men, and 
of the men have brown eyes. If 
of the people have brown eyes, then what fraction of the group are women who do not have brown eyes