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如图所示,在坐标系xOy平面的x>0区域内,存在电场强度大小E=2×105N/C、方向垂直于x轴的匀强电场和磁感应强度大小B=0.20T、方向与xOy平面垂直向外的匀强磁场.在y轴上有一足够长的荧光屏PQ,在x轴上的M(10,0)点处有一粒子发射枪向x轴正方向连续不断地发射大量质量m=6.4×1027kg、电荷量q=3.2×1019C的带正电粒子(重力不计),粒子恰能沿x轴做匀速直线运动.若撤去电场,并使粒子发射枪以M点为轴在xOy平面内以角速度ω=2πrad/s顺时针匀速转动(整个装置都处在真空中).

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    Bob was happy. He was at a new school, and the other students were friendly. “Hi, Bob!” they said. But some students said, “Hi, Peter!” Bob didn't understand. He asked another student, “Why do some students call me Peter?”
    “Oh, that's easy to answer,” the students said. “Peter was a student here last year. Now he goes to a different school. You look like Peter. Some students think that you're Peter.”
    Bob wanted to meet Peter. He got Peter's address from a student and went to Peter's house. Peter opened the door. Bob couldn't believe his eyes. He looked really like Peter! Bob and Peter had the same colour eyes and the same smile. They had the same black hair. They also had the same birthday. And they both were adopted(领养) by two different families.
    Bob and Peter found out that they were twin brothers. Soon after the boys were born, one family adopted Bob, and another family adopted Peter. Bob's family never knew about Peter, and Peter's family never knew about Bob.
    Bob and Peter's story was in the newspaper. There was a photo of Bob and Peter next to the story. A young man named John saw the photo in the newspaper. John couldn't believe his eyes. He looked really like Bob and Peter! He had the same colour eyes and the same smile. He had the same black hair. He had the same birthday. And he, too, was adopted by another family.
    Later John met Bob and Peter. When Bob and Peter saw John, they couldn't believe their eyes. John looked really like them! Why did John look really like Bob and Peter? You can guess. Bob and Peter are not twins. Bob, Peter and John are triplets(三胞胎).
    Choose the best answer: