英语周报七年级第六期（2019～2022）答案

18.解:(1)存在一点F,使得平面SAD∥平面BEF,此时F为CD的中点;证明:∠BAD=∠CDA=90°,故AB∥CD又F为CD的中点,且AB=CD,所以FD=AB,故四边形ABFD是矩形,∴AD∥BF,又BF(平面SADADC平面SAD,BF∥平面ASD2分E,F分别为SC,CD的中点,∴EF∥SD,,EF∥平面ASD3分又EF∩BF=F,∴平面ASD∥平而BEF(2)由SA⊥平面ABCD,结合(1)可以以A为坐标原点,以AB,AD5分AS所在直线为x,y,z轴建立空间直角坐标系Axyz,设AB=1,则B(1,0,0),D(0,2,0),S(0,0,A),C(2,2,0),故)从而=(-1,20),B=(01,)7分设平面BCD的法向量为m1=(0,0,1),平面BDE的法向量为m2=(x,y,z)x+2y=0则B2=0,取y1,可得m=(21,-29分设二面角E-BD-C的大小为0,因为A>0,则cos0=|cos(m1,m2)|=2√4,解得入=222+1+

The"novel"coronavirus, being called 2019-nCoV offihacpn detectedbefore the outbreakted in Wuhan, China in December, 2019. Infection with 2019-nCoVwascan cause mild symptom including a runnysore throat, cough, and fever. It can be mostsymptonevefor some persons and cause pneumonia or breathing difficulties: More rare, the disease carelybe deadly. It can be transmitted from person to person, usually after close contact with A infectedpatient that even seems healthyTo proteet,yoHrst, wash your hands frequently with soap and water. Maintain at least 1meter: distant between yourself and other people, particularly those who are coughing anddistancesneezing. Wear a medical mask can help limit the spread of some respiratory IfF B) diseasesWearingTherefore, it has to be combined to other prevention measures including washing hands andHoweverwithavoiding close contact to take effect【解析】笫一处错误: called2019- n Cov officiallyy充当后置定语。 being called,.“正在被称作……”,不符合语境。第二处错误:根据时间状语 in december,2019可知应用一般过去时。第三处错误:根据后文列举的多种症状 a runny nose, sore throat, cough and fever可知此处应改为名词复数 symptoms第四处错误:根据上下文语意,应用比较級。第五处错误: more rarely:“更少见的(是)……”,修饰句子,用副词。第六处错误: patient为可数名词单数, , infected发音以元音音素开头,所以前面加不定冠词an第七处错误: maintain distance:保持距离。第八处错误;动名词充当主语。第九处错误:根据句意作出修改。笫十处错误: A is combined with B。

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