．人类生活需要能量。下列能量主要由化学变化产生的是 （ ）
A．电水壶烧开水时需要的热量
B．水电站利用水力发出的电能
C．点燃的酒精灯放出的热能
D．风力发电站所利用的风能
C
题目分析：化学变化是指有新物质生成的变化．物理变化是指没有新物质生成的变化．化学变化和物理变化的本质区别是否有新物质生成．
A、电水壶烧水的过程中没有新物质生成，属于物理变化．故选项错误．
B、水力发电的过程中没有新物质生成，属于物理变化．故选项错误；
C、酒精燃烧能生成水和二氧化碳，属于化学变化．故选项正确；
D、风力发电的过程中没有新物质生成，属于物理变化．故选项错误．
点评：解答此类题型时，在掌握能量来源和利用的基础的同时，可以借用排除法进行筛选，即可选出正确的答案．
 Everyone wants to have healthy teeth. When you laugh, you will 1 your mouth and show your teeth. The healthier your teeth are, the happier you feel. Why is that? It's 2 your teeth are important in many ways. Take care of them, and they'll help to take care of you. Strong, 3 teeth help you grow. They also help you speak clearly. You can take pate of your teeth by doing like these: Brush your teeth 4 a day, after getting up and before bedtime. And you brush all of your teeth, not just the front ones. Spend some time 5 the teeth along the sides and in the back. Take your time while brushing. Spend at 6 three minutes each time you brush. Be sure your toothbrush is soft. Ask your parents to help you get a new toothbrush 7 three months. Clean between your teeth with dental floss(牙线).I t feels strange when you do it at first, but soon you'll get used to 8 it. Brushing 9 your teeth healthy. You also need to care about what you eat and drink. Eat 10 fruits and vegetables and drink water instead of drinks. Do you want to have white and healthy teeth? Please brush your teeth!
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