高一外研英语周报23答案

17.【解析】(1)由an-bn=2"得a2=b2+4=5,a4=b4+16=9,2分设{an}的公差为d,则d=4a2=2,a1=a2-d=3…分则{an}的通项公式为an=a1+(n-1)d=3+(n-1)×2=2n+1.………………4分因为bn=an-2",…5分则S=(a1+a21+…+a)-(2+2+…+2)(3+2n+1)2×(n2+2n-2m++2…6分21-2(2)设{b}的公比为q,当q=2时,{an}是等比数列,当q≠2时,{a}不是等比数列分下面进行说明2+4(2)解法一:由题意知an=2"+b,-=…4分2"+b2+a(2)2则3,=4,.整理得A(2)(9)=一2则一,解得b22=09-q因此当q=2时,{an}是等比数列公比也是212分解法二:由题意知an=2”+b,由a2n1=an,an+2得(2+bn1)2=(2+bn)(22+bn2),……9分因为b21=bb2整理得22bn1=2b2+22b,则4q=q2+4,解得q=2,……………11分因此当q=2时,{an}是等比数列.……………………2分解法三:若{an}是等比数列则a2=a4,即(b2+4)=(b+2)(b+8)灬………8分即b2+8b2+16=b+8b1+2b+16,即4b2=4b+b,即4bq=4b+bq,解得q=210分当q=2时,an=b2+2”=(b+2)2,因为h>0,所以=世=2(常数),故{an}是等比数列12分

【语篇类型】一记叙文【主题语境】人与自我一助人经历【文章大意】本文讲述了作者在芝加哥偶遇一个无家可归的人并施以援手的故事。【核心素养】语篇以作者帮助一个无家可归的人为背景,展示了人性的闪光点和生活中的真善美,助力考生树立正确的价值观,体现了文化意识这一核心素养。郾熟词新义1.dow常用义:淋浴文章义:大量给予He showered her with gifts.他送给她许多礼物。2. finance常用义:n.资金;财政,金融,财务文章义:t.为……提供资金The concerts are financed by the Arts Council.音乐会由艺术协会出资举办词汇积累 flash back(osh.)回忆,回想,回顾;(尤指电影、书等)闪回,倒叙Her thoughts flashed back to their wedding day.她回忆起他们婚礼那一天的情景。难句分析1 only had a few dollars left in my wallet,,. but I went tobu连接两个并列句him directly, bent down and handed them to this fellow, talking withhim, touching his hand and wishing him well before I left现在分词短语作伴随状语before引导时间状语从句译文:我的钱包里只剩下几美元了,但在我离开前,我径直走到他面前,弯下腰,把钱递給他,并和他交谈,抚摸他的手,祝他一切顺利。4.D【关键能力】考查理解具体信息的能力。【解题思路】根据第二段的" a man sitting on the sidewalk..Mymind flashed back and I realized I had seen a homeless person oncebefore:Me"可知,作者在外出散步时看到了一个无家可归的人,这使他想起了自己无家可归的经历。5.c【关键能力】考查推理判断的能力。【解题思路】根据第三段的" the home I grew up in caught fire in themiddle of the night. I can still remember the fire destroyed everythingwe owned ""our small town communitytemporary house"可知,作者的家遭遇火灾,大火烧毁了他们的一切使他们无家可归。第二段的" I had seen a homeless person oncebefore:Me"也是提示。6.D【关键能力】考查理解具体信息的能力。【解题思路】根据第四段的" I only had a few dollars left in mywallet, but I went to him directly, bent down and handed them to thisfellow, talking with him, touching his hand and wishing him well beforeI left"可知,作者把身上仅有的几美元都给了那个无家可归的人,且和他交谈,安慰了他。7A【关键能力】考查推理判断的能力。【解题思路】根据最后一段的内容可知,作者一直并且将继续帮助他人,作者认为即使自己所能做的非常有限,但只要人人付出点,世界就会变得更好。结合上文中的“ Thankfully, our small towncommunity showered us with love and care""I could remember feelingloved even after losing so much"可推知,作者感恩于自己得到的爱与关怀,也希望将其传递下去故选A项”关爱使世界更美好”。B项”人之初性本善";C项"不尝试,不知晓”;D项"凡事要肯等待"。

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