问题 选择题

在平面直角坐标系xOy中,已知A(2,-2),在y轴上确定点P,使△AOP为等腰三角形,则符合条件的点有                      (      )

A.2个

B.3个

C.4个

D.5个

答案

答案:C

分二种情况进行讨论:

当OA为等腰三角形的腰时,以O为圆心OA为半径的圆弧与y轴有两个交点,以A为圆心AO为半径的圆弧与y轴有一个交点;

当OA为等腰三角形的底时,作线段OA的垂直平分线,与y轴有一个交点.

∴符合条件的点一共4个

故选C.

单项选择题
完形填空

As my train was delayed for two hours, I had plenty of time to spare. After buying some newspapers to read on the journey, I made my way to the ___1___ office to collect my heavy suitcase I had ___2___ there three days before. There were only a few people ___3___, and I took out my wallet to find the receipt for my case. The receipt didn’t seem to be where I had left it. I ___4___ the contents, and railway tickets, money scraps of paper and photos fell out of it; but no matter how ___5___ I searched, the receipt was nowhere to be found.

When my turn came, I ___6___ the situation sorrowfully to the assistant. The man looked at me ___7___ as if to say that he had ___8___ this kind of story many times and asked me to ___9___ the case. I told him that it was an old, brown looking ___10___ no different from the many cases I could see on the shelves. The assistant then gave me ___11___ and told me to ___12___ of the chief contents of the case. If they were ___13___, he said, I could take the case away. I tried to ___14___ all the articles I had ___15___ packed into the case and wrote them down as they came to me.

After I had done this, I went to ___16___ among the shelves. There were hundreds of cases there. For one dreadful moment, it ___17___ to me that if someone had ___18___ the receipt up he could have easily claimed(认领) the case already. This hadn’t happened ___19___, for after a time I found the case lying in a corner. After examining the articles inside, the assistant was ___20___ and told me I could take the case away.

1. A. posting   B. working     C. luggage      D. manager’s

2. A. left B. forgotten    C. found  D. bought

3. A. standing B. crowding    C. talking       D. waiting

4. A threw      B. put     C. looked       D. emptied

5. A. often      B. much  C. hard    D. soon

6. A. said B. searched     C. spoke  D. explained

7. A. now and then B. up and down      C. here and there    D. back and forth

8. A. knew      B. realized      C. heard  D. seen

9. A. describe  B. draw   C. take out      D. show

10. A. object   B. matter C. subject       D. wallet

11. A. a paper B. a note C. a message   D. a form

12. A. sign names   B. make a list  C. write down D. draw a picture

13. A. everything   B. wrong C. correct       D. ready

14. A. draw    B. remember   C. read    D. remind

15. A. carelessly     B. suddenly    C. hurriedly    D. immediately

16. A. see       B. watch  C. find    D. look

17. A. happened     B. occurred     C. appeared    D. seemed

18. A. picked  B. collected    C. taken  D. stolen

19. A. fortunately   B. unluckily    C. by chance   D. presently

20. A. disappointed B. surprised    C. satisfied     D. worried