2020到2022，七年级上册英语周报答案

ll.BC【解析】对于A选项,勒洛四面体面积最大的截面即经过四面体ABCD表面的截面,如图1,则勒洛四面体的截面面积的最大值为三个弓形加上一个正三角形,知A错误;对于B选项,由勒洛四面体的结构知B正确;对于C选项,所有面的交线长的和为6个圆心角为,半径为4的弧长的和,故6××4=8x,故C正确;对于D选项,正四面体ABCD棱长为a=4,M是底面BCD的中心,O是其外接球(也是正四面体的中心)的球心外接球半径为R,AM是高,如图2.BM=2×原×4=4,AM=AB=BM=46,33,由B0BMF OMF得F=(—-R) (),解得R一后勒洛四面体能够容纳的最大球与勒洛四面体的弧面相切,如图3,其中点E为该球与勒洛四面体的一个切点,O为该球的球心,易知该球的球心O为正四面体ABCD的中心,半径为OE,连接BE,易知B,O,E三点共线.可得BE=4,OB=6,因此OE=BE-OB4-√6,故D错误B∈ M图版权所有Cm图3

第一节参考范文:Last Friday evening witnessed a breathtaking English Singing Contest in our schoolstadium, where 15 singers competed for"The Best English Singer of the YearThe singers, who had stood out from the first round of selection, gave energeticperformances on stage. Throughout the contest, the atmosphere in the stadium was extremelyexciting, with many students singing along to nearly every song. At last, the award went toZhang Xin from Class 1 Grade 1Everyone agreed that the contest enriched our campus life as well as kindling ourpassion for English learning

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