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实验桌上有高度不同的发光物体A和B,焦距分别为5cm、10cm的凸透镜两个,刻度尺、光具座和光屏各一个.小华选用这些器材,探究“凸透镜成实像时,像的高度与凸透镜的焦距是否有关”.小华的主要实验步骤如下:

①将焦距为10cm的凸透镜固定在光具座中央,将发光物体A、光屏分别放在凸透镜两侧.调节发光物体A、凸透镜和光屏的高度,使它们的中心在同一高度.

②将发光物体A放在光具座上距凸透镜30cm处,移动光屏,在光屏上得到发光物体A清晰的像,用刻度尺测量像的高度,并记录在表格中.

③用发光物体B替换A放在光具座上距凸透镜30cm处,移动光屏,在光屏上得到发光物体B清晰的像,用刻度尺测量像的高度,并记录在表格中.

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阅读下面短文,从短文后各题所给的A、B、C和D四个选项中,选出可以填入空白处的最佳选项。

    The late Booth Tarkington always said, “I could take anything that life could force upon me except one thing: blindness. I could never 1 that.”

    One day, when he was along in his sixties, Tarkington 2 down at the carpet on the floor. The colors were not clear, so he went to a 3, and he soon learned the truth: he was losing his sight. What he4 most had come on him. And 5 did Tarkington react to it? To his amazement, he felt quite 6. When total darkness closed in, Tarkington even said, “I found I could take the 7 of my eyesight, just as a man can 8 anything else. If I lost all five of my9, I know I could live on inside my mind. For it is in the mind we see, and in the mind we live, whether we know it or not.”

    To 10 his eyesight, Tarkington had to go through over twelve operations within one year. He knew he couldn't 11 it, so the only way to lessen his 12 was to accept. And when he had to have 13 operations, he tried to remember how fortunate he was. He said, “How wonderful it is that 14 now has the skill to operate on anything so 15 as the human eye!”

    A(n) 16 man would have been nervous if he had had to tolerate over twelve operations and 17 Yet, Tarkington said, “I wouldn't 18 this experience for a happier one.” It taught him 19. It taught him that nothing life could bring him was 20 his strength to tolerate.