题目

在下图所示的电场中，a、b两点的电场强度和电势均相同的是( )A. 离点电荷等距离的a、b两点B. 两个等量异种点电荷连线的中垂线上，与连线中点等距离的a、b两点C. 两个等量同种点电荷连线上，与连线中点等距离的a、b两点D. 带电平行金属板间分别靠近两板的a、b两点 答案：【答案】B【解析】试题A项是负点电荷形成的电场，a、b是离点电荷等距的两点，处在同一等势面上，电势相同，场强大小相等，但方向不同，故A错；B项是等量异种电荷连线的中垂线是一条等势线，则a、b的电势相等。由于电场线关于两电荷连线左右对称，而且都与等势面垂直，所以a、b两点的场强大小Everyone knows that flamingos are tropical birds. A resident of Ottawa, however, spotted a flamingo one cold November day. The bird, called Elisha, was more than 300 miles from home when she landed in Ottawa. Elisha was living in a bird compound in a small town near Connecticut when she got lost. Why was the bird flying around? “She was probably trying to migrate,” says a naturalist. “A flamingo’s natural instinct is to migrate to warmer weather in winter.” For the past few years, Elisha has lived in a bird compound with other birds, ducks, and swans. In summer, the birds spend their time in a shallow pond. In winter they live in a large, heated greenhouse. One day, Elisha took off and flew about 50 miles to the Connecticut River. Her caregivers tried to get her back and planned to clip（夹住）her wings so she wouldn’t fly away again. But every time they approached, Elisha managed to get away. “That’s a smart bird,” said a news reporter. “She probably knew she was about to get her wings clipped.” Back in Ottawa, wildlife experts were trying to rescue Elisha before she froze to death. But it wasn’t easy. First they put up a giant mirror to attract her and placed plates of food next to her. Next, they gathered together plastic flamingos . They set the plastic birds up in a park nearby,  “We were hoping that Elisha would like being in a group, even if it is plastic. Maybe she would fall in love or something,” a rescue worker said. That didn’t work either. “She’s not easy to catch, ” said a compound worker in Connecticut. “We couldn’t catch her either. She seems to like her freedom.” Finally, after a dozen rescue attempts by almost 100 volunteers, Elisha was captured. “I guess she got hungry,” said a rescue worker. “We were about to give up when we saw her looking for food at the edge of the river. She couldn’t find anything to eat because the water was frozen. ” Elisha put her head in the water to feed. When she came up they caught her in a net. Then she flew back to Connecticut, this time by plane. 1．Why was Elisha found in Ottawa in November?       A．She was meant to find something to eat.        B．She got lost in an attempt to migrate.        C．She intended to stay away from a bird group.        D．She had to land in Ottawa for a break. 2．Which of the following was NOT used when people tried to catch Elisha?        A．A large mirror.                                     B．Plates of food.        C．Plastic flamingos.                                D．Ducks and swans. 3．What can we learn from the text?        A．It is more than 300 miles away from Ottawa to Connecticut.        B．Two attempts had been made before Elisha was captured.        C．Elisha was almost frozen to death when caught in a net.        D．Rescue workers gave up their effort to catch Elisha. 4．What can we infer from the text?       A．Elisha didn’t like her caregivers and managed to get away.        B．Connecticut is a tropical area.        C．The rescue of Elisha cost a lot of money.        D．Elisha would never try to leave her group again. 5．Which of the following can be the best title for the passage?        A．The Lost Flamingo                               B．Lost & Found        C．Bird Rescuers                         D．Flamingos