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电磁铁的磁性有无可用电流的通断来控制，除此之外，电磁铁和永久磁铁比较，优点还有______。

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根据各组对话内容，从下面方框中提供的5个选项中选出能填入空白处的最佳选项。A. It was great. B. What"s the matter C. How about the green oneD. Are you free tomorrow E. Thanks, but I am full. A: So many nice coats! I can"t decide which one to buy. B: ______

根据各组对话内容，从下面方框中提供的5个选项中选出能填入空白处的最佳选项。A. It was great. B. What"s the matter C. How about the green oneD. Are you free tomorrow E. Thanks, but I am full. A: Helen. The happy weekend is coming. ______ B: Yes. I"m not busy at all. I"ve already finished my homework.

自然界中有许多奥妙的声现象。声音是人们交流信息的重要渠道，是日常生活中经常接触到的物理现象。下列有关声现象的说法错误的是______。

A. 用牙齿听声音利用的是骨传导
B. 用超声波能击碎人体内的结石，说明声波具有能量
C. 利用声波和电磁波都可以传递信息
D. 市区内某些路段“禁鸣喇叭”，这是在声音传播的过程中减弱噪声

根据各组对话内容，从下面方框中提供的5个选项中选出能填入空白处的最佳选项。A. It was great. B. What"s the matter C. How about the green oneD. Are you free tomorrow E. Thanks, but I am full. A: Help yourself to some dumplings. B: ______