如图，某侦察机在空中A处发现敌方地面目标B，此时从飞机上看目标B的俯角为α，已知飞行高度AC=4500米，tanα= $\frac{\sqrt{5}}{6}$，则飞机到目标B的水平距离BC为（　　）

“吾人果欲于政治上采用共和立宪制，复欲于伦理上保守纲常阶级制，以收新旧调和之效，自家冲撞，此绝对不可能之事。盖共和立宪制，以独立、平等、自由为原则，与纲常阶级制为绝对不可相容之物，存其一必废其一。”上述言论最有可能出自于（    ）

提出问题：蚕总是吃桑叶，这是先天性行为吗？

根据短文内容，从A、B、C、D四个选项中选择正确答案填空。

    Children often  1 this game. They play it like this: Six 2 stand in a row(排) 3 the class. They put their hands 4 their backs(背), so you can't see their hands. The teacher gives one of them 5 rubber. The rubber goes 6 one student to another -- first one way, then the other. They must keep their hands behind their backs. The other students in the class keep their eyes    7. They can't look.

    Then the teacher says: “Stop and put your hands  8 you now.” Now the other students 9 their eyes, and guess who has the rubber. They ask questions like: “Li Lei, is it in  10 right hand?” They can have only five guesses.

地幔中的岩浆在某个固定位置上具有强烈上升的趋势，称之为热点。当板块薄弱点经过热点时形成火山喷发，称为热点火山。随着板块移动，热点火山在板块表面留下一连串火山锥（如图所示）。图中热点位于甲点的（    ）