实验课上，小明同学把一包铜粉和锌粉的混合物放入一定量的硝酸银溶液中，使其充分反应后过滤，得到固体和蓝色滤液。下列判断中正确的是
A．滤出的固体中一定含有银，可能含有铜
B．滤出的固体中一定含有银和铜，一定不含锌
C．滤液中一定含有硝酸铜，一定没有硝酸锌和硝酸银
D．滤液中一定含有硝酸锌和硝酸铜，一定没有硝酸银
答案：A
充分反应后溶液为蓝色，此现象可说明铜和硝酸银发生了反应；因为锌活动性大于铜，可知在铜开始与硝酸银反应时锌已经完全反应，则滤出的固体中一定含银、一定不含锌，如果铜过量固体中可能含有铜，而滤液中一定含硝酸锌和硝酸铜、如果硝酸银过量，滤液中可能含有硝酸银；故选A
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| Bertha Ingram had been collecting them for more than 40 years. Every once in a while she would bring home a new book She'd sit with it on her leg, looking at the meaningless black marks without moving the eyes and cry. She was not stupid. She simply had not had the 1 to learn to read. Her parents were sharecroppers in Florida in the 1920s. Sharecroppers did not own the 2 they farmed. Instead, they gave a part of their crops (plants grown on farms for food) to the owner. It was quite a hard way to 3 , and both of Bertha's parents worked hard in the fields. Often Bertha had to leave school to help. Before she was a teenager, Bertha's schooling was 4 . Bertha Ingram didn't learn to read 5 her early married life, either. She wanted to, but she was always too busy. She worked all day. Bertha Ingram's mind was sharp (敏锐的). As a housekeeper for other people, she had to memorize telephone messages. She became a good cook too, but she had to 6 everything she did because there was no cookbook she could read, and she couldn't write down what she had done. In 1978 Bertha Ingram became very ill with a stroke (中风). This illness 7 her to lose the use of one arm and both legs. It also weakened her ability to speak. 8 she began to get better, she had a 9 thought - for the first time in her life. Because she couldn't work, she had the time to learn to read. In her town there was a special program that taught adults to read, but Bertha Ingram was quite nervous. Would people laugh at her? Would they 10 to teach her? It didn't happen that way. She had a teacher who worked very hard with her. After the first day Ingram could 11 wait to get to the library. As she learned to read, Ingram got more and more confidence (信心) in herself. She became a reader at religious (宗教的) services, joined neighborhood groups, and 12 at meetings in the city hall. Finally she wrote a book telling about her life. At age 63, Bertha Ingram proved that learning never comes too late. | ||||
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