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问题 问答题 简答题

三相桥式全控整流电路有何特点，其触发脉冲有何要求？

答案

参考答案：三相桥式全控整流电路，六个桥臂元件全都采用可控硅管。它既可工作于整流状态，将交流变成直流；也可工作于逆变状态，将直流变成交流。其触发脉冲的宽度均大于60°，即所谓“宽脉冲触发”，或者采用“双脉冲触发”。

选择题

人类将在未来几十年内逐渐由“碳素燃料文明时代”过渡至“太阳能文明时代”（包括风能、生物质能等太阳能的转换形态）。下列不符合这一主题的是

A．减少一次性用品的使用

B．利用太阳能蒸馏海水进行海水的淡化

C．避开公共交通的拥挤，倡导自驾出行

D．海水和淡水交汇处安装半透膜，利用水中电解质浓度的差异进行发电
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问答题

Have you had a headache during a test Have you ever been so worried about something that you have a headache or even can’t sleep at night If so, then you know what stress is. Stress is what you feel when you are worried about something. This worry in your mind can make your body feel bad. You may feel angry, sad, scared, or afraid—all of which can give you a stomachache or a headache.
However, there are different kinds of stress. Some kinds of stress are good and others are bad. Good stress might happen when you’re called to answer questions in class or when you have to give a speech. This kind of stress can help you to get things better done. For example, you may do a better job on your test if the stress pushes you to prepare better before the test.
On the other hand, bad stress can happen if stress lasts too long. You may not feel well if your parents are fighting, if a family member is sick, if you’re having problems at school, or if anything else makes you unhappy every day. That kind of stress isn’t going to help you. And it can actually make you sick.
The best way to fight stress is to have a balanced life. Make sure you keep your SELF in mind: Sleep, Exercise, Leisure(休闲), and Food. If you get enough sleep and eat properly, and if you exercise and leave time for fun, you’ll probably feel less stressed.

Title: Face the Stress
Meaning of stressStress is a　(68)　when you are worried about something.
Possible effectYou may feel uncomfortable in your　(69)　and body.

Good stress

· It might happen when you have to　(70)　in public.

· It will be more　(71)　for you to do the job successfully.

· It makes you　(72)　better before doing the job.
Different kindsBad stress

· It might happen if your stress　(73)　too long.

· You may not feel well with the　(74)　of a family member, problems at school or something else that worries you every day.

· It might stop you from getting your work well done.
How to keep stress　(75)　

Have a balanced life.

· Have enough sleep and have　(76)　food.

· Take exercise and have time to　(77)　yourself.

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