为了验证声是由振动的物体产生的，有的同学做了以下几个实验，不正确的是（ ）
A．录音机扬声器上放上纸屑，放录音时纸屑随之“跳舞”
B．使正在发声的音叉接触水面，水面溅起水花
C．吹笛子时，手指按住不同的孔便会发出不同的声音
D．在吊着的大钟上固定一支细小的笔，把钟敲响后，用纸在笔尖上迅速拖过，可以在纸上画出一条来回弯曲的细线
A、录音机扬声器上放上纸屑，放录音时纸屑随之“跳舞”，能验证声是由振动的物体产生的．
B、使正在发声的音叉接触水面，水面溅起水花，能验证声是由振动的物体产生的．
C、吹笛子时，手指按住不同的孔，即改变了笛子内空气柱长度，改变空气柱振动的频率，笛子发声的音调改变．是验证声音的音调与频率有关的实验，故C不能验证声是由振动的物体产生的．
D、在吊着的大钟上固定一支细小的笔，把钟敲响后，用纸在笔尖上迅速拖过，可以在纸上画出一条来回弯曲的细线，能验证声是由振动的物体产生的．
故选C
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| These days it is found that school students hardly have any sports. Is it because they have no 1 in sports? It may not be true. They often say they have much more important things to do. What are these important things? Exams! They have to 2 themselves ready for all kinds of exams and tests in school. So many of them almast become bookworms (书呆子). In the past in the sununer holidays, they could do everything they liked,but now they have to 3 all their time preparing their lessons. So 4 have kept them away from sports. 5 their parents and teachers give them morepressure (压力), they have to work _6 and spend most of their time on books. As for the students themselves, they don't want to 7 in the exams because they want to further their studies. So it is necessary to give all of their spare time to their studies and 8 up their school sports. It's true that a good education can not go withoutphysical training (体育锻炼). A quick mind hardly goes along with a 9 body. Without a strong body,you can never do anything well, and 10 can you make great success in life? | ||||
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