题目

在等比数列{an}中，前n项和Sn=2n+c，则a12+a22+a32+…+an2等于_______________. 答案：(4n-1)  解析：当n≥2时，an=Sn-Sn-1=2n-1，∵{an}是等比数列，∴a1=1，公比q=2.∴{an2}也是等比数列，首项为1，公比为4，∴a12+a22+a32+…+an2==(4n-1).Our teacher assigned “secret friends” for the coming week. Its purpose was to do ____ things for your “secret friends” without letting them know. She wrote each kid’s name on a piece of paper, threw them into a bucket and ____ from the bucket the name of the classmate who we were to befriend ____ the next five days.By the middle of the week, everyone in my class, including me, had turned this assignment into a ____ to see whose secret friend could give the best ____. On the last morning of our assignment, I ____ a package on my desk. Then I opened it and there ____ a can of perfumed powder (香粉).The girls sitting near me ____ the “old lady gift”. To make matters worse, the powder had already been opened.I tried to forget the ____ gift. But when the same girls gossiped about it again during the ____ in the bathroom, I quickly ____. “How stupid! My grandmother wouldn’t even want it,” I said angrily. After the girls left, I thought about what I had just said. It wasn’t normally like me to say ____ things like that.Hearing a creak (嗅吱声)，I turned around to ____ Rochelle, a girl from my class. There were tears ____ down her face. “I’m your secret ____,” she whispered to me. “I’m sorry about the gift.” Then she ran out of the bathroom.I was sick to my stomach as my cruel ____ ran through my mind. It took me a few days ____ I finally found the courage to face up to Rochelle and ____. She told me that her family couldn’t afford a fancy present and her mother had ____ her only luxury so that Rochelle could have something to give to me.On that day, I learned to show respect for people like Rochelle—people who give from the ____.【1】A. active B. curious C. nice D. awful【2】A. drew B. touched C. gathered D. learned【3】A. honestly B. generously C. openly D. secretly【4】A. delight B. agreement C. shame D. competition【5】A. gift B. wish C. help D. promise【6】A. unfolded B. noticed C. accepted D. scanned【7】A. lay B. floated C. moved D. came【8】A. take care of B. laughed at C. yelled at D. stick out of【9】A. special B. expensive C. embarrassing D. awesome【10】A. month B. break C. class D. night【11】A. looked down B. stood up C. went away D. joined in【12】A. mean B. thoughtful C. wonderful D. vivid【13】A. greet B. see C. ignore D. wait【14】A. cutting B. pulling C. streaming D. washing【15】A. partner B. teacher C. friend D. deskmate【16】A. information B. idea C. explanation D. words【17】A. and B. but C. so D. for【18】A. tolerate B. forgive C. apologize D. complain【19】A. promised B. sold C. used up D. given up【20】A. heart B. hand C. package D. home