问题
不定项选择
| 不定项选择 |
| 下列关于交变电流的说法正确的是（ ） |
| A．交变电流的大小和方向都一定随时间变化 B．交变电流的有效值就是平均值 C．线圈平面跟磁场垂直时，穿过线圈的磁通量最大，而感应电动势为零 D．线圈平面跟磁场平行时，穿过线圈的磁通量为零，而感应电动势为零 |
答案
答案：C
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| 不定项选择 |
| 下列关于交变电流的说法正确的是（ ） |
| A．交变电流的大小和方向都一定随时间变化 B．交变电流的有效值就是平均值 C．线圈平面跟磁场垂直时，穿过线圈的磁通量最大，而感应电动势为零 D．线圈平面跟磁场平行时，穿过线圈的磁通量为零，而感应电动势为零 |
答案：C
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| Helen Keller lived in the USA. She was a great woman. When Helen was a baby, she got very ill. After many weeks, the doctor said, "She is better, but now she can't see and she can't hear." Her mother and father were very sad. After a few years, things got worse (更糟糕). There was no way for Helen to speak to other people. She heard nothing. She saw nothing. She didn't understand anything. Then one day a teacher came to live with Helen and her family. The teacher helped Helen learn about words. Helen was a very bright girl and soon she learnt to spell her first word. When she was older, she went to college (大学). Helen was very famous (著名的). She helped many blind (盲) and deaf (聋) people. 阅读短文，根据短文内容填写表格，每空一词。
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