问题 单项选择题

利用( )原理进行热设计,难以降低电子产品周围的环境温度。

A.热传导

B.对流

C.热辐射

D.人工制冷

答案

参考答案:D

解析: 产品特别是电子产品周围的环境温度过高是造成其故障率增大的重要原因。因此应利用热传导、对流、热辐射等原理结合必要的自然通风、强制通风、以致水冷及热管等技术进行合理的热设计,以降低其周围的环境温度。

阅读理解

根据短文内容,选择最佳选项.

    I suppose when you grow up in one place, you have friends whom you've known since childhood.

But as a child who moved a lot, my oldest friendships are with my cousins.

    On our return from Guam, my parents, sisters and I walked off the plane in Alexandria. All my cousins

were there to meet us.

    I was excited to see them again. The last time I'd seen Don, Sherri and David was two years before.

That summer we'd caught fireflies(萤火虫) and watched Don and his friends play a game. Some boys

acted like a bull(公牛) with a rope(绳子). His friend held the rope and Don rode on it. When Don fell

off, he got up and tried again.

    Just like riding that bull, Don put his heart into everything he did. As a young man he was told he got

cancer(癌症). But he fought it and never gave up. Like what he did that summer, he held tight(紧紧地),

falling off a few times and trying again. I was excited and proud of my cousin for planning and going after

his dream. I wished his ride would have lasted longer.

1. The writer and his family returned to Alexandria      .

A. by boat              

B. by ship

C. by air                

D. by train

2. The writer and his cousins       in the summer two years ago.

A. became good friends

B. moved to Guam

C. rode a bull

D. caught fireflies

3. What does the underlined word "held" mean in the passage?

A. 抓住    

B. 容纳    

C. 扣留    

D. 举办

4. When did Don know he got cancer?

A. When he was born.

B. When he was a young man.

C. Two years ago.

D. Last summer.

5. From the last paragraph, we know Don is a man who        .

A. is very shy            

B. never gives up

C. has a bull              

D. is very foolish

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