高一英语周报68期19-20答案

应用文写作One possible versionDear Mr GreenI'm writing to ask you for a favorI'm preparing an English speech with the title"Cloning's role in Life. I hope I can getpeople to think more about the significance of cloning and the potential problems it may causeHowever, when it comes to the moral risks cloning may bring us, I find it quite hard to make myewpoint convincing enough, as I lack solid evidence and relevant knowledge. So I wonder if yoould recommend some books sharing experts arguments on this topicLooking forward to your early replyLIH

15.【解析】(1)带电粒子在y轴左侧磁场中均做半径为D的匀速圆周运动,则r=D(1分)由qUB=m1分)可得B=mv(2分)D(2)由题意可得,所加磁场的形状如图所示通过磁场区域时间最长的是沿磁场边缘运动的粒子在左边磁场中的时间为t1=T_丌D(2分)2U在右边磁场中的时间为t=4=27(2分)总时间为t=2+t2=x(D+d(2分)(3)磁场的最小面积Sm=4(xD2-)D2)+4(4a_B)=(2)(D+d2)(2分

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