如果等腰三角形两边长是6和3，那么它的周长是（ ） A．9 B．12 C．15或

已知圆C的方程是（x-1）²+（y-1）²=4，直线l的方程为y=x+m，求：当m为何值时

（1）直线平分圆；

（2）直线与圆相切；

（3）直线与圆有两个公共点．

如肤色偏红的部位（）抑制色。

A.红的

B.紫色

C.绿色

D.黄色

An analyst gathered information about three economic variables. He noted that whenever variable A increased by one unit, variable B increased by 0.2 units but variable C decreased by 0.7 units. The correlation between variables A and B and the correlation between variables A and C, respectively, are closest to: Correlation between variables A and B Correlation between variables A and C（）

A. 1.0                   -1.0 

B. 1.0                   -0.5 

C. 0.5                   -1.0

玉米矮花病防治方法。

从性质上看，治安耳目可以分为红色耳目和（）