如图，一玻璃柱体的横截面为半圆形，细的单色光束从空气射向柱体的O点(半圆的圆心)，产生反射光束1和透射光束2，已知玻璃折射率为 ，入射角为45°(相应的折射角为24°)，现保持入射光不变，将半圆柱绕通过O点垂直于图面的轴线顺时针转过15°，如图中虚线所示，则 (　　)

如果方程组 $\{\begin{array}{c}x=y+1\\ 2x-y=2\end{array}$ 的解是方程3x﹣4y+a=6的解，那么a的值是____．

用所给动词的正确时态、语态填空
⑴Be quiet, please ! The baby____ (sleep).
⑵—What does Frank often do at weekends?
—He often____ (go) to the cinema with his parents.
⑶Andy ____ (argue) with his brother when I went to see him yesterday.
⑷She ____ (be) to her hometown several times.
⑸____ (play) computer games too much is bad for your eyes.
⑹Lucy tried ____(not make) too many mistakes in the exam.
⑺He ____  to us as soon as he gets there. (write)
⑻By the time I got outside, the bus____ (leave).
⑼I'm sure I ____  her four years ago. (see)
⑽In summer,  Miss Xia would rather ____  (stay) at home than go out.

下列属于复杂反射的是（　　）

如图表示神经、免疫、内分泌三大系统调节人体生理活动的部分示意图．下列说法正确的是（    ）