如图所示，平行板MN、PQ间距离为d，板长为2d，板的正中有一半径为 $\frac{d}{2}$ 的圆形有界磁场，磁场边界刚好与两板相切，两板间所加电压为U，一质量为m，电量为q的带电粒子从左端沿两板间的中线向右射入两板间，若只撤去磁场，粒子刚好从上板右端N点射出，若只撤去两板间所加的电压，带电粒子恰好能从下板的右端Q点射出，不计粒子的重力，求：

    Many kids don't drink enough water daily, according to a new study. The study's lead author, Erica Kenney, at first planned to look into the amount of sugary drinks kids were drinking in schools. However, during her research she found that many kids were simply not drinking enough water.

    Kenney and her team examined data from a group of 4,000 children, aged 6 to19. The data was taken from the National Health and Nutrition Survey, a study on the health of children in the United States done each year by the Center for Disease Control and Prevention.

    While looking through the survey results, she noticed that more than half of the kids who took part in the study were dehydrated (脱水的). Of that group, boys were 76% more likely than girls not to have enough water in their system. Nearly one quarter of the kids in the survey reported drinking no plain water at all.

    “These findings highlight (突出) a possible health issue that wasn't given a lot of attention in the past,” Kenney said in a statement. “Even though for most of these kids this is not an immediate and great health risk, this is an issue that could really be reducing quality of life and well-being for many children and youth.”

    The United States-National Agriculture Library says average kids need between 10 to 14 cups of water every day. This water can come from a mix of drinks and foods that contain high amounts of water, such as celery, melons or tomatoes. It is also suggested that fluids (液体) come from water instead of sugary drinks that are high in calories and can lead to weight problems.

既是两大洲分界线又是两大洋分界线的海峡是

      A passenger（乘客）told an air hostess that he needed a cup of water to take his medicine when the plane just took off. She said to him that she would bring him the water in ten minutes.
The air hostess was kept so busy that she forgot to give him the water. As a result, the passenger was held up to take his medicine. Thirty minutes later, when the passenger’s ring for service sounded, the air hostess hurried over to him with a cup of water, but he refused it.
In the following hours on the plane, each time the air hostess passed the passenger, she would ask him with a smile whether he needed help or not. But the passenger never replied to her.
       When the passenger was going to get off the plane, he asked the air hostess to hand him the passenger’s booklet. She knew that he would write down sharp words about her job, but with a smile she handed it to him.
Off the plane, the air hostess opened the booklet, and smiled because the passenger wrote, “On the flight, you asked me whether I needed help or not for twelve times in all. How can I refuse your twelve sincere smiles?”