问题 填空题

如图所示,水平面上有一个平面镜与桌面成a角,有一个小球正向镜前滚去,若镜中的小球的像恰好沿竖直方向下落,则角a为 ______;若要使小球的像刚好也在桌面上滚,则角为 ______.潜望镜是利用平面镜 ______并 ______的.

答案

此时小球在桌面上,而小球的像竖直向下,所以物与像的夹角为90°,根据平面镜成像的特点,而平面镜可将像与物体的夹角平分,所以物与平面镜的夹角为45°,即平面镜与桌面的夹角为45°,故答案为:45°;

当小球的像也在桌面上时,物与像的夹角为180°,平面镜可将像与物体的夹角平分,所以物与平面镜的夹角为90°,即平面镜与桌面的夹角为90°,故答案为:90°;

潜望镜是由两块平面镜组成的,平面镜成像是根据光的反射原理,平面镜可改变光的传播方向,并成正立等大的虚像,

故答案为:改变光路,成像.

完形填空

Though different educational systems have different purposes, one thing is certain: all students should take part in examinations.

___1___ the English educational system, students take ___2___ very important ___3___. The first is the eleven-plus, which is taken at the age of eleven ___4___ past. At one time the ability ___5___ on the eleven-plus would have determined ___6___ a child stayed in school. ___7___, however, all children continue in “comprehensive”(综合性的) schools, and the eleven-plus determines which courses of study the child will follow. At the age of fifteen or sixteen, the students are tested for the Ordinary Level of the General Certificate(证书) of Education. This examination covers a wide ___8___ of subjects; once students have passed this exam, they are ___9___ to specialize, so that two-thirds or ___10___ of their courses will be ___11___ physics, chemistry, classical language, or ___12___ they wish to study ___13___. The ___14___ examination, at eighteen, covers only the ___15___ of the special subjects. ___16___ the universities, students study only in their concentrated area, and ___17___ students ever venture(冒险) outside ___18___ subject again; ___19___, the English boy or girl is a specialist ___20___ the age of fifteen.

1. A. On  B. In       C. To      D. For

2. A. four       B. three   C. two     D. one

3. A. subjects  B. languages   C. courses       D. examinations

4. A. somewhat      B. or else C. or so   D. or rather

5. A. seen       B. heard  C. shown D. known

6. A. when      B. if C. that     D. how

7. A. But B. Then   C. So      D. Now

8. A. number  B. part    C. range  D. collection

9. A. allowed  B. passed C. forbidden   D. admit

10. A. much    B. many  C. more   D. most

11. A. in  B. of       C. with    D. on

12. A. whenever     B.however      C.whatever D. wherever

13. A. at all costs    B. at the same time      C. at the least   D. at great length

14. A. late      B. later    C. early   D. final

15. A. context B. content         C. book   D. lesson

16. A. Even so       B. Even if      C. Even then   D. Even at

17. A. few      B. no      C. some   D. any

18. A. that      B. their   C. its       D. which

19. A. in any case   B. in all C. in a sense   D. in the end

20. A. of B. from C. at       D. under

单项选择题