直流电动机利用 ____的原理制成，把 ____能转化为 ____能。直流电动机的换向器的作用是每当线圈转过 ____位置时，它就能自动改变 ____的方向，使线圈不停地转动。
生产实际和实验室有很多金属材料．
Hello. I am Amy. I am eight years old. Today is my birthday. Look, I have a birthday cake. I have juice and rice for dinner. And I have many gifts, too. A red toy monkey, two new bags and five storybooks. I am so happy today.
