题干

在数学课上,老师提出如下问题:
已知:如图, ΔABC 及AC边的中点O,
求作:平行四边形ABCD
小敏的作法如下:
①  连接BO并延长,在延长线上截取OD=BO
②  连接DA、DC,
所以四边形ABCD就是所求作的平行四边形。

老师说:”小敏的作法正确.“
请回答:小敏的作法正确的理由是____.
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答案(点此获取答案解析)

对角线互相平分的四边形是平行四边形

同类题3

阅读下列短文,根据短文内容填写表格。(每空限填一词)

    We have only one earth. It is the only environment for humans, animals and plants to live or grow in. However, we are polluting our earth every day. Good news is that the whole world has realized the serious problems and has taken action to fight against it.

    World No Tobacco Day (May 31)

    The first World No Tobacco Day is April 7, 1988. Since 1989, it was changed to be May 31st every year. The purpose of the World No Tobacco Day is to encourage people not to smoke.

    World Water Day (March 22, 1993)

    United Nations named 22 March as the first World Water Day in 1993. It's a day to celebrate water. It's a day to prepare for how we manage water in the future. It is celebrated around the world every year.

Earth Hour ( 2007)

    Earth Hour started for the first time on March 31, 2007 in Sydney, Australia. Since then, the last Saturday of every March was named as Earth hour day that year. On March 19, 2016, more than 350 famous buildings in 178 countries around the world turned off the lights for one hour to remind people to save electrical power.

    Actions in China to save our environment

    Smoking is not allowed in all indoor public places from 2014.This is the first time for China to care about personal health in public places.

    Ban(禁令) on free plastic bags. Since June 1, 2008, free plastic shopping bags are not allowed to provide in all supermarkets, shopping malls, and other places. It is to encourage people to use cloth bags or baskets for their shopping things.

Theme:The only environment for all the____ things has serious problems, but the whole world has done____to prevent pollution.

Actions around the world

No Tobacco Day

Started on April 7,1988,then changed to May 31st every year. Encourage people to ____ up smoking.

World ____ Day

Started on March 22nd 1993, celebrated around the world every year.

Earth Hour

Started for the____ time on March 31st 2007, turned off lights for an hour to____ electrical power.

Actions in ____

Public places

Smoking is allowed in____ public places to care about personal health.

Supermarket &

Shopping malls

Encourage people to ____ cloth bags or baskets for shopping things. You need to____if you use plastic bags provided by the supermarket.

同类题5

阅读下面选段,完成题目。
                                                                                                  成长,有时只是瞬间的事
        人们常说“少年不识愁滋味”,然而16岁的我,心中总有挥之不去的忧愁。由于长期疏于学业,我的成绩一直在低处徘徊。尽管在众人面前我总是故作坦然,但心里却有难言的苦涩。我想,我不像其他同学那样聪明!
       然而,那一堂极其普通的美术课,却无意中颠覆了我对自己的认识。
       那堂美术欣赏课,讲的是法国印象派画家莫奈。周五,又是下午第一节。很多同学都埋着头,用美术课本遮掩因犯困而迷糊的眼神。夏日的午热混杂着少年的汗味弥漫在教室里;窗外的老柳树似乎懒得再摇曳,蝉儿却很高调地重复着昨天的老歌;远处传来繁忙的市音,隐隐约约,嘈嘈杂杂……
      也许只是为了打破昏昏欲睡的沉闷,年轻的美术老师说:“我请一位同学谈谈对这幅画的感受。这样吧,姚远同学,你来说说。”我没想到,被喊中的人是自己,迟迟疑疑地站起来。周围有窃窃的笑声与私语。
        (A)我的心,因为那些轻蔑的话语而猛烈地跳动,手不自觉地攥紧了。我真想冲那些自以为是的同学说一句:住嘴!可是,我什么也说不出来,只是下意识地低头,再低头,想把自己滚烫的脸,埋进深深的臂弯。
        我当时的样子,一定很窘迫、很无助。美术老师轻轻地走到我旁边:“姚远同学,是不是不舒服?”老师侧着脸,关切地看着我。我摇摇头,双手很奇怪地卷着书角,然后展开,再卷起,好像一点点铺排着内心的局促、不安……
        老师帮我把书角展平,指着那幅画说:“你好好看看,感觉到了什么?”是那幅莫奈的《睡莲》:水波粼粼,睡莲的叶子或聚或散,花朵像暗红的、摇曳的火焰,热烈而又含蓄。看似随意的柔美线条,捕捉住了水面似真似幻的光和影。看着那画,我心里竟有一种隐隐的感动。沉默良久,我听见自己用极不确定的语气说:“画家好像是想表现……温和、平静、美丽的大自然。”
       只是几个字而已,美术老师却很欣赏地说:“说得好!莫奈的画,总是善于捕捉大自然的美丽。”她轻轻地按了按我的肩膀:“你挺有悟性的。这幅画,藏于法国奥赛博物馆,希望有一天,你能去亲眼看一看。”我愣住了,确定这句话是专门说给我听的!我定定地看着老师走向讲台的背影,满心的喜悦里夹杂一丝疑虑,“老师说我挺有悟性的!老师真的是这么说的!可老师这是在鼓励后进生吗?也许……”
        接下来欣赏的是莫奈的《干草垛》。我凝视着这幅画,用心感受着画意。我敢说,我从未这么专心地上过课!老师先请后排一位同学谈观感,那同学只说画面太单调了。老师微笑地点评:“莫奈画的虽只是干草垛,却巧妙地描绘了光与色带给人的视觉印象。斜射的阳光下,淡橙的天空,橙紫的远山,橙绿的树林,橙黄的干草垛……阳光在跃动,色彩在变幻。画面虽简单,却有一种不同寻常的生命力。”我聚精会神地听着,默默地将老师的讲析与自己的观画印象一一对照。我发现,自己的观画印象竟然与老师的讲析大致吻合,只是我的感受稍显稚嫩。这一发现,让我惊喜万分!
        那个周末,烈日流火。我兴冲冲地跑到艺术品商店,买了一幅带画框的《睡莲》。虽只是临摹画,我的喜悦却是那样真实而强烈。
        我告诉父亲,这是美术学科的参考资料。(B)父亲意味深长地看了我一眼,点点头,什么也没说,只是爬到椅子上,郑重其事地帮着把画挂在我的房间里。
          我开始了一个人的战争,和自卑作战,和惰怠作战。我还一遍遍地为自己勾画未来的蓝图。越来越多的人真诚地用“阳光”、“自信”、“上进”这些词来形容我。
          终于,我鼓起梦想的翅膀,飞向远方……
         大学时,我主修国际金融,但我对莫奈的画却始终有一种难以名状的亲切感,就连我的父母对莫奈的画都有特殊的感情。那幅《睡莲》,从我16岁那时起就一直挂在我的房间里。
         再回故乡时,我想找到那位美术老师,告诉她,法国的奥赛博物馆我已经去过了。不过,毕竟是男子汉了,有些细节我会不好意思说的,比如,那天在奥赛博物馆里,面对莫奈《睡莲》真迹,我竟流下了热泪!