问题 问答题 简答题

什么叫雷电反击?预防雷电反击方法。

答案

参考答案:

雷电流流过正常情况下处于低电位的导体(包括接地装置),造成电位升高,引起该导体向正常情况下处于高电位、或低电位的导体放电的现象,叫雷电反击。

预防雷电反击的方法有:采用共用接地或瞬态共用接地方式

论述题
阅读理解

For years I wanted a flower garden. I spent hours and days thinking of different things I could plant that would look nice together.

But then we had Matthew. And Marvin. And the twins, Alisa and Alan. And then Helen. Five children. I was too busy raising them to grow a garden.

Money was tight, as well as time. Often when my children were little, one of them would want something that cost too much, and I’d have to say, “Do you see a money tree outside? Money doesn’t grow on trees, you know.”

Finally, all five children got through high school and college and were off on their own. I started thinking again about having a garden.

I wasn’t sure, though. I mean, gardens do cost money, and after all these years I was used to living on a pretty poor, no-frills budget (预算).

Then, one spring morning, on Mother’s day, I was working in my kitchen. Suddenly, I realized that cars were tooting their horns as they drove by. I looked out of the window and there was a new tree, planted right in my yard. I thought it must be a weeping willow, because I saw things blowing around on all its branches. Then I put my glasses on—and I couldn’t believe what I saw. There was a money tree in my yard!

I went outside to look. It was true! There were dollar bills, one hundred of them, tied all over the tree. Think of all the garden flowers I could buy with one hundred dollars! There was also a note attached: “IOU eight hours of digging time. Love, Marvin.”

Marvin kept his promise, too. He dug up a nice ten-by-fifteen foot bed for me. And my other children bought me tools, a trellis (绷架), a sunflower stepping stone and gardening books.

That was three years ago. My garden’s now very pretty, just like what I wanted. When I go out to weed or tend my flowers, I don’t seem to miss my children as much as I once did. It feels like they are right there with me.

I live up in Michigan’s Upper Peninsula, where winters are long and cold, and summers are too short. But every year now, when winter sets in, I look out of my window and think of the flowers I’ll see next spring in my little garden. I think about what my children did for me, and I get tears in my eyes---every time.

I’m still not sure that money grows on trees. But I know love does.

小题1:By saying “Do you see a money tree outside?”, the mother actually means _____.

A.Observation is the best teacher

B.Seeing is believing

C.The outsider sees the most of the game

D.It is not easy to gain money小题2:The underlined word “no-frills” in the fifth paragraph is similar in meaning to _____.

A.wasteful

B.tight

C.deserted

D.helpful小题3:From the last two paragraphs we can infer that the mother is _____.

A.divorced when she was young

B.not caring for her kids any longer

C.alone but not at all lonely

D.prouder with her garden than with her kids小题4:The best title for the passage would probably be _____.

A.My flower garden

B.Marvin helps to realize my dream

C.Love in Michigan

D.Money grows on trees