问题 选择题
如图所示为一磁流体发电机示意图,A、B是平行正对的金属板,等离子体(电离的气体,由自由电子和阳离子构成,整体呈电中性)从左侧进入,在t时间内有n个自由电子落在B板上,则关于R中的电流大小及方向判断正确的是(  )

A.I= ,从上向下

B.I= ,从上向下

C.I= ,从下向上

D.I= ,从下向上

答案

答案:A

实验题
阅读理解

阅读理解。

     It doesn't make any difference how long your speech is. Unless you tune in the first 60 seconds, the

chances are they will tune you out.   

     Take the fellow who opens: "On my way over to the club tonight, I ran into a bum (流浪汉) who asked

me for $ 49.50 for a cup of coffee. I told him he'd do much better if he asked for a quarter. He said, 'Do

you think I'm going into the Ritz in these clothes?'" We know his purpose: to win his audience over with

humor. His bit of humor, however, has no connection with his speech. He has his audience laughing at the

wrong time. Once you have an audience laughing it's hard to get them to switch to an entirely different train

of thought. There is nothing wrong with humor in a speech as long as it has something to do with the purpose

of his speech. To open a speech with humor just to be entertaining invites an almost sure"turnoff" for the

remainder of the talk.  

1. What, in a speech, determines its failure or success?   

A. The purpose of the speech.     

B. A sense of humor.   

C. The opening remarks.       

D. A forceful ending.  

2. If a speaker decides to be humorous, his humor should _________.   

A. be connected with his subject      

B. make his audience laugh   

C. be fresh and different          

D. be reserved for the end  

3. What do the underlined words mean?   

A. bring your speech to an end

B. cause your audience to lose interest   

C. make your audience go away at once

D. have your audience laugh with you  

4. Which of the following best expresses the main idea of the passage?  

A. The opening part of your speech should not be long.   

B. Humor is important in the success of your speech.   

C. Your humor should be relevant (相关的) and timely.   

D. An outstanding speech is full of jokes.