问题 选择题

下图表示光学显微镜的一组镜头,目镜标有5×和15×字样,物镜标有10×和40×字样。最低放大倍数的一组镜头是:(   )

A.① ③

B.① ④

C.② ③

D.② ④

答案

答案:B

题目分析:显微镜的放大倍数是目镜和物镜放大倍数的乘积,所以最低放大倍数的一组镜头是5×的目镜和10×的物镜,由于物镜的镜头越长,放大倍数越大,镜头越短,放大倍数越小,所以选①和④。

点评:此题为基础题,有关显微镜使用方面的题都很重要,要想做好此类题目,一定要多动手,多思考,熟能生巧。

单项选择题
阅读理解

阅读理解。

     My family lived in Baltimore. One summer evening as I was fixing supper, there was a knock at the door.

I opened it to see a truly terrible-looking man."Why, he's hardly taller than my eight-year-old," I thought as I

stared at the stooped (弯腰屈背的) body.

      Yet his voice was pleasant as he said,"Good evening. I've come to see if you've a room for just one night.

I came here for a treatment this morning form the eastern shore, and there's no bus till morning." He told me

he'd been hunting for a room since noon but with no success. No one seemed to have a room."I guess it's my

face. I know it looks terrible, but my doctor says with a few more treatments…"

      I told him I would find him a bed. I went inside and finished getting supper. When I was ready, I asked the

old man if he would join me. "No, thank you. I have plenty." And he help up a brown paper bag.

     When I had finished the dishes, I went out on the porch (走廊) to talk with him for a few minutes. It didn't

take a long time to see that this old man had an oversized heart crowded into that tiny body. He told me he

fished for a living to support his daughter, her five children, and her husband, who lost his legs in a car

accident.

     At bedtime, I put a bed in the children's room for him. When I got up in the morning,the bed linens (床单)

were neatly folded and the little man was out on the porch. He refused breakfast, but just before he left for his

bus, haltingly (犹豫不决地), as if asking a great favor, he said,"Could I come back and stay the next time I

have a treatment? I can sleep fine in a chair." I told him he was welcome to come again.

1. The man came to Baltimore to ______.

A. visit his son.

B. see a doctor

C. find a job

D. hunt for a room

2. Nobody would take the man in because ______.

A. he was very poor

B. he was from the eastern shore

C. he was a man of strange appearance

D. there was no extra room

3. Which of the following is TRUE about the man?

A. He was one of the author's close friends.

B. He had trouble finding the author's home.

C. He wore an oversized coat.

D. He was a great father.

4. From this passage we know that the author is ______.

A. brave

B. kind

C. clever

D. rich