问题
问答题
平面镜前有一点光源s，做出一条从光源s射出的光线，使它经平面镜反射后，恰好经过A点．
答案
过镜面作出点S的对称点S′，即为点光源S在平面镜中的像，连接S′A与镜面交于O点，即为入射点（反射点），连接SO就得到入射光线，如下图所示：
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平面镜前有一点光源s，做出一条从光源s射出的光线，使它经平面镜反射后，恰好经过A点．
过镜面作出点S的对称点S′，即为点光源S在平面镜中的像，连接S′A与镜面交于O点，即为入射点（反射点），连接SO就得到入射光线，如下图所示：
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| Do you think everyone 1_their weekends? Old Henry does 2_. Last month, he went 3_ a walk with Wang Wang, his cute dog. It was a nice day and Old Henry was happy. He 4 on a bench and watched Wang Wang 5 _a friendly black cat. Years before, when Wang Wang was young, his wife was also there. They always walked 6_ the weekend… Then it was time to go home. Old Henry 7_for his dog."Wang Wang!" But Wang Wang wasn’t there… | |||
| ( )1. A. enjoy ( )2. A. not ( )3. A. to ( )4. A. sit ( )5. A. play ( )6. A. over ( )7. A. looking ( )8. A. sad ( )9. A. not ( )10.A. didn’t | B. enjoyed B. no B. for B. sits B. playing B. on B. looks B. happy B. any B. don’t | C. enjoys C. any C. on C. sitting C. to play C. at C. to look C. luck C. no C. doesn’t | D. enjoying D. so D. in D. sat D. played D. to D. looked D. lucky D. some D. isn’t |