问题 填空题

某细胞在培养过程中,每15分钟分裂一次(由1个细胞分裂成2个),则经过两个小时后,1个这样的细胞可以分裂成______个.

答案

由于每15分钟分裂一次,则两个小时共分裂8次.

一个这样的细胞经过一次分裂后,由1个分裂成2个;经过2次分裂后,由1个分裂成22个;

经过8次分裂后,由1个分裂成28个.

∴1个这样的细胞经过两个小时后,共分裂成28个,即256个.

故答案为:256

单项选择题 共用题干题
阅读理解

Students often want to practice their English outside class. One of the best ways to practice your English is to speak to a foreigner. You may ask, “Is it okay to try to talk to foreigners I see in the street?”

The answer is yes and no, but probably no! If you see a foreigner who looks lost, it is polite to ask him, “May I help you?” But, otherwise, you should probably let them get on with their business. Situations, however, do exist where it is quite all right to talk to foreigners. If a foreigner enters your school, classroom, office, shop or restaurant, for instance, feel free to ask him (for example):

— What is your name?

— Where do you come from?

— What do you think of Beijing?

— How long will you stay in Beijing?

There are also situations where it's okay to talk to foreigners in public places. If you see a foreigner alone in a restaurant, bar or coffee shop, it may be appropriate to ask him or her:

— Is this seat free?

— Do you mind if I talk to you in English?

You can probably help them if they are new in China and if they are alone, you may be able to make them feel more welcome.

After a few such questions, you should know whether this person wants to talk to you or not. If they ask you similar questions, or if they give long, informative answers, you're in luck. If not, then give them their privacy. Talking to strangers is fun if you choose the right time and place.

66. It is the best way to practice your spoken English with ______.

A. Japanese           B. Americans                C. our classmates           D. French people

67. From the second paragraph we can get to know that ______.

A. it is polite to stop a foreigner to talk with him in the street

B. it is polite to interrupt foreigners in a conversation

C. it is impolite to interrupt a foreigner when he or she is on business

D. it is impolite to help a foreigner find his way

68. When you first meet a foreigner, you should say “_______”

A. Where are you going?                           B. Have you ten your dinner?

C. Can you help me with my English?         D. Nice to meet you.

69. The writer suggests to us that we should ______.

A. follow the foreigners when we meet them in the street

B. talk with a foreigner in an accepted way

C. have a meal with foreigners in a restaurant

D. move to a place where a foreigner lives

70. This passage comes from a newspaper in column ________.

A. Sports               B. Health               C. Language                 D. Business