在面向对象方法中，属性与操作相似的一组对象称为 【2】 。

Mr. Black used to ________ a teacher. But now he is a writer.

[      ]

A. /

B. is

C. be

D. being

已知a-b=2，a-c=1，求（2a﹣b﹣c）²+（c﹣a）²的值．

脑组织的能量来源于______。

A．蛋白质

B．脂肪

C．碳水化合物

D．碳水化合物和脂肪

E．蛋白质和碳水化合物

There are robots all around us. Some do very complicated jobs like flying airplanes and driving subway trains. and some do one simple job. When an automatic washing machine is switched on, water pours in. The machine waits until the water is warm enough for washing clothes. It does this by “feedback”(反馈). Information about what is happening is feedback into the robot to tell what to do next. Our eyes, ears and other senses are our feedback. They tell us what is going on around us. So robots are like human beings in two ways.

They work and they have feedback.

In some ways robots are better than human beings. They work quickly and do not make mistakes. They do not get bored doing the same job over and over again. And they never get tired. So robots are very useful in factories. They can be taught to do many different jobs. First their electronic brain must be shown how the job is done. A person moves the robot’s “arms” and “hands” through each part of the job.

The most intelligent robots can move and see. Their eyes are cameras. Their fingers can feel shapes and sizes of the objects. These robots have computer brains linked to their eyes and fingers, which control their actions. The expensive robots are used in scientific research. They do such job as handling radioactive materials.

小题1: In this passage the author tells us that ________.

A．robots are very popular

B．there are various kinds of robots

C．we see robots only at certain times

D．robots can be easily controlled小题2:What does the author seem to inform you about robots?

A．They should be greatly improved.

B．They will probably take over in the future.

C．They are very helpful and useful to humans.

D．They are machines that break down a lot.小题3:The author says that in industry ________.

A．robots break down a lot

B．robots can do many jobs

C．robots only get in the way

D．robots sometimes cause troubles小题4: The fact that a robot never gets bored doing the same job means that _______.

A．it is very much like human beings

B．it can do boring jobs for people

C．it will never bore people

D．it will work much better than human beings小题5: The robots used for scientific research _______.

A．are not very clever

B．are very cheap

C．are very big

D．are very costly

生油岩的岩石类型有哪些？生油岩的岩性特征是什么？