一自耦变压器如图所示，环形铁芯上只饶有一个线圈，将其接在a、b间作为原线圈。通过滑动触头取该线圈的一部分，接在c、d间作为副线圈。在a、b间输入电压为U1的交变电流时，c、d间的输出电压为U2，在将滑动触头从M点顺时针旋转到N点的过程中（）。
A.U2＞U1，U2降低
B.U2＞U1，U2升高
C.U2＜U1，U2降低
D.U2＜U1，U2升高
参考答案：C
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| If you often have a cold, headache or backache, there is something wrong with your health. Eating healthy food 1 good for our health. Tofu (豆腐), milk, vegetables are healthy for us. Tofu is a kind of traditional (传统的) 2 food. We often 3 it in China. Now more and more people 4 other countries think tofu is good for health, 5 . They also like eating it. Milk is 6 kind of health food. Every day you should 7 one or two glasses of milk. It can 8 us strong. Vegetables are very important. You should eat 9 them. There are vitamin (维他命) A, B, C, D, E and so on in them. As we know, it's important 10 a balanced diet (均衡饮食). We must have the right kinds of food. We should also eat some pork, chicken and beef. We should eat more fruit and vegetables but less meat. | ||||
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