1、选择题  在真空环境中，原来匀速直线运动的电子进入到与它运动方向垂直的匀强磁场中，在洛伦兹力的作用下，形成圆弧运动轨迹，下面的说法中正确的是（　　）
A．电子所受的洛伦兹力是恒力
B．进入磁场后电子动能不变
C．进入磁场后电子的动量不变
D．若加一个方向与磁场方向相反的匀强电场后，就有可能使电子沿直线运动

2、选择题  如图所示，A、B为水平正对放置的平行金属板，板间距离为d．一质量为m的带电油滴在两金属板之间，油滴运动时所受空气阻力的大小与其速率成正比．将油滴由静止释放，若两金属板间的电压为零，一段时间后油滴以速率v匀速下降．若两金属板间加电压U，一段时间后油滴以速率2v匀速上升．由此可知油滴所带电荷量的大小为（　　）
A.style="shiti/data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACAAAAApCAIAAADbF7xrAAAAqUlEQVRIie2VURKAIAhE9/6Xpr+0YFFJm1L5clT2gYJCBhs2YEIAACDJDsng54BcPQHOg9ODm3NueokCGEOv2mHiHmg5Aw1g5+BsuwDYoEkxDpDsAhywDWDqfu7axdxDAWaROPM0RTMuFqYfrO0bAJgzjwDitlgfQNgul9PXXsxgA54DWIHWVG1LRZtPTaknGhotoL4OIKy+FEB3QI1jLUDk4//BBkwOOADtmKAX/s0SBgAAAABJRU5ErkJggg==" alt="">
B.style="shiti/data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACcAAAArCAIAAAB0AwYZAAAAvUlEQVRYhe3VSxaAIAgFUPa/aRp5SnmAilQDGHn83Ugp4i+CSi211FmJiIhGlVqkwp36xPJgkGu22iXmDLd3LhvDkmfIIUfVdlTX94wk8TRbhSnOMM40gxweNsRoKrxErspKyRmncKvwMbXGTJlpJzqq8hLCBjx4o5/RywiVpnb1/IUHVdhzXmXz+5Co7kV32u/Ep7mW+itVq5Ol4tnMFe6eW69BstRsslRXlZW6vMnqAubNf2pUjUeppZ6LC6RKlVqAVRzSAAAAAElFTkSuQmCC" alt="">
C.style="shiti/data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACUAAAAmCAIAAADMaMX6AAAAs0lEQVRYhe3VSw7AIAgE0Ln/pemqP2FQrLRJAytjxFdUUsi7gfLK6xkAgNPDHqnkaevZRM+cTcJuXoMdJ6wHepl5I9fE1nP2opn3FI3Zy2jhVlkjQGdZN8fEAsAqT0gjOWdOPTYYaR52c80n2pfvJPvP8nr39L2MB3v6/cQlnjmz0hO301O8ucCb8UV95X3lsdcfaolwfea+Wf33ECtvLVZes7XuvBAW80Qm/3nz3vP4u7cBFC9xVBpO5tkAAAAASUVORK5CYII=" alt="">
D.style="shiti/data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACcAAAAoCAIAAADyl3S3AAAAt0lEQVRYhe3V0Q6AIAgF0P7/p+3B5gy4DFS0NXhyKhwtrauciCvVVFd4NdBYLIyWs1WtPXHqU9+itt3zBp/WAlWgapuKKvJ8Miqm92WpqqfxLVoY1KbrFR8Rl7wMVFEVi9ovWlmNQ0Wksicx9zV/TBVfvNJP26LqCnT0tJTlqtizXi3q9yFQ9YZ2XwPj8F5T/Y6KjsWOmyNWNx7PQXWGTDWaTNWi8pvqqzCgFvaDcqePqZOR6j/VG2DBNK2MQVLRAAAAAElFTkSuQmCC" alt="">