A little boy invited his mother to attend his school’s first teacher-parent meeting. To the little boy’s __1__, she said she would go. This __2__ be the first time that his classmates and teacher __3__ his mother and he felt __4__ of her appearance. Although she was a beautiful woman, there was a severe scar (疤痕) that __5__ nearly the entire right side of her face. The boy never wanted to __6__ why or how she got the scar.
At the meeting, the people were __7__ by the kindness and natural beauty of his mother __ 8__ the scar, but the little boy was still embarrassed (尴尬) and __9 __ himself from everyone. He did, however, get within __10__of a conversation between his mother and his teacher.
The teacher asked __11__, “How did you get the scar on your face?”
The mother replied, “__12__ my son was a baby, he was in a room that caught fire. Everyone was __13__ afraid to go in because the fire was __14__，so I went in. As I was running toward his bed, I saw a long piece of wood coming down and I placed myself over him trying to protect him. I was knocked __15__ but fortunately, a fireman came in and saved both of us.” She __16__ the burned side of her face. “This scar will be __17__, but to this day, I have never __18__ what I did.”
At this point, the little boy came out running toward his mother with tears in his eyes. He held her in his arms and felt a great __19__ of the sacrifice (牺牲) that his mother had made for him. He held her hand __20__ for the rest of the day.
1. A. enjoyment B. disappointment C. surprise D. excitement
2. A. would B. could C. should D. must
3. A. noticed B. greeted C. accepted D. met
4. A. sick B. ashamed C. afraid D. tired
5. A. included B. passed C. covered D. shaded
6. A. talk about B. think about C. care about D. hear about
7. A. impressed B. surprised C. excited D. comforted
8. A. in sight of B. by means of C. by way of D. in spite of
9. A. hid B. protected C. separated D. escaped
10. A. understanding B. reminding C. hearing D. learning
11. A. carefully B. seriously C. nervously D. anxiously
12. A. As B. When C. Since D. While
13. A. so B. much C. quite D. too
14. A. out of control B. under control C. in control D. over control
15. A. helpless B. hopeless C. senseless D. useless
16. A. pointed B. showed C. wiped D. touched
17. A. ugly B. lasting C. serious D. frightening
18. A. forgot B. recognized C. considered D. regretted
19. A. honor B. sense C. happiness D. pride
20. A. quietly B. slightly C. tightly D. suddenly
，可见弹性模量E越大，音速a越大。 对于气体，，可见音速与密度对压强的变化率的平方根成反比，即流体越容易压缩，音速a越小。对于不可压缩流体，音速a为无穷大。 [解题关键] 声音的传播是一种小扰动波，密度对压强的变化率与小扰动波的传播速度有密切关系。音速n是流体的一个重要参数。