点群

工料单价法中，最主要也是最常用的计算程序的计算基础是（）。

A.直接费

B.人工费

C.机械费

D.人工费和机械费

(16分)如图所示，在平面直角坐标系xoy中的第一象限内存在磁感应强度大小为B、方向垂直于坐标平面向里的有界圆形匀强磁场区域(图中未画出)；在第二象限内存在沿x轴负方向的匀强电场．一粒子源固定在x轴上坐标为(－L，0)的A点．粒子源沿y轴正方向释放出速度大小为v的电子，电子恰好能通过y轴上坐标为(0，2L)的C点，电子经过磁场偏转后恰好垂直通过第一象限内与x轴正方向成15°角的射线ON(已知电子的质量为m，电荷量为e，不考虑粒子的重力和粒子之间的相互作用)．求：

⑴匀强电场的电场强度E的大小；

⑵电子离开电场时的速度方向与y轴正方向的夹角θ；

⑶圆形磁场的最小半径R_min．

阅读理解。

                                                                    Count Me Out 

     Call me old-fashioned. Call me old. Call me what you want, but I refuse to become part of this new

Internet world.

     I do not possess a computer at home or at the office. Actually, I stopped going to an office 35 years ago,

when all communications were done with a pen, a typewriter, or, if the matter was of world-shaking

importance, over the telephone. Likewise, if you like something advertised in a newspaper or magazine, you

visited the shop selling it at the given address, or you phoned the number shown. Then you spoke to the fellow

and asked for further details.

     Tell me what you think of the following ad that appeared the other day in the newspaper. It was for a cure

for cancer and this is what it said: "Awareness is the key. Visit spfulford. com at the awareness site." There

was no address or telephone number for the site. So what do unfortunate people without a computer do if they

are seeking a cure for their illness?

     There are, I am told, certain advantages in having access to the Internet. You can, for example, send love

messages across the world or even get married to someone that you meet online. This bit doesn't interest me;

I have been happily married for 60 years. There are, of course, other activities for Internet users besides finding

love. They can pay bills, order groceries, or discuss with their doctors.

     And this is by no means all. More amazing things are yet to come in the near future. I read a newspaper

report recently that quoted Stephen Hawking, an important British scientist. "The complexity of a computer as

it exists today is probably less than the brain of an earthworm," he said. "But, as technology advances,

computers will become more complex, and a time may come when the Internet may develop 'consciousness.'

In other words, the Internet will be able to think, have feelings, and may well be able to act on its own."

     If Professor Hawking is right, I may change my attitude to computers. As I grow older each day, I would

like one of those that not only thinks for me but also accepts responsibilities for all my mistakes.

1. What's the meaning of the title "Count Me Out"?

A. Get me out of the Internet world.

B. Computers are trying to take control of life.

C. Modern technology pushes old people away.

D. Do not expect me to be a supporter of the Internet.

2. According to Paragraph 2, the author thinks computers are _____.

A. unnecessary

B. convenient

C. expensive

D. advanced

3. What might the author like about the future computer?

A. Taking blames.

B. Curing illnesses.

C. Delivering messages.

D. Responding to emotions.

我国大气污染的特点是什么？