题目

磁流体发电机是利用运动电荷在磁场中偏转发电的,如图是它的示意图．平行金属板 A、B之间有一个方向垂直于纸面向里的磁场,将一束等离子体(即高温下电离的气体,含有大量正、负带电粒子)从左向右喷入磁场,A、B两板间便产生电势差．下列判断正确的是（） A . A板电势高于 B板，负载 R 中电流向下 B . A板电势高于 B板，负载 R 中电流向上 C . B板电势高于 A板，负载 R 中电流向下 D . B板电势高于 A板，负载 R 中电流向上Everybody hates rats. But rats may soon be man’s new good friends.What happens after an earthquake? We send in rescue(援救)dogs. Why? Because they can smell people. Dogs save lives. They help rescuers to find living people. But dogs are big and they can’t get into small spaces. So now a new research project is using a smaller animal to save lives： the rat.How does it work? First， the rat is trained to smell people. When this happens， the rat’s brain gives a signal(信号). This is sent to a small radio on its back， and then the rescuers follow the radio signals. When the rat’s brain activity jumps， the rescuers know that someone is alive. The rat has smelled that person.Although there are already robots which can do this job， rats are better. “Robots’ noses don’t work well when there are other smells around. Rats are good at that.” Rats can also see in the dark， they are cheaper and quicker to train than dogs， and unlike robots， they don’t need electricity!The “rat project” is not finished， but a scientist says， “It would be great. A rat could get into spaces we couldn’t get to， and a rat would get out if it wasn’t safe.” Perhaps for the first time in history， people will be happy to see a rat in a building (but only after an earthquake， of course).1.In the writer’s opinion， rats may become man’s new friends because .A. they can be food for peopleB. they can help rescuers to find living peopleC. they are lovelyD. they can completely take the place of man to carry out rescue jobs2.What does the underlined word “this” mean?A. An earthquake.B. The rat has smelled a personC. The rat has smelled that someone is alive .D. The rat has found a robot.3.Which of the following is NOT true?A. Rats don’t need electricity.B. Rats are better than robots when smelling.C. Rats are as clever as radios.D. Rats can see things in the dark when doing rescues.4.Why does the “rat project” sound great according to the passage?A. Because rats can get into very small spaces.B. Because rats have better noses than dogs.C. Because rats don’t like robots.D. Because rats are brave.5.Which is the best title of this passage?A. Ways of saving people B. Rats and robotsC. After earthquake D. Rats for rescue