题干

如图所示,小华把悬挂的铁锁拉近并紧贴自己的鼻子,稳定后松手,头保持不动,铁锁向前摆去又摆回.下列说法正确的是(  )

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A:锁不断地来回摆动,是因为动能不断增加

B:锁向下摆的过程中,重力势能转化为动能

C:锁摆到最低点后会继续上升,是因为受重力作用

D:锁摆动的过程中,机械能总量不变,所以摆回来时会碰到鼻子

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B

同类题1

完形填空

     George selected his food in Value Mart carefully. He estimated he had180cents today.He was pleased he had got good2for his money again.

      At the exit,the freezing wind3him of his gloves.He was sure he was wearing them whenentering the4.He made a search of his pockets.Then he thought theymust have been5somewhere in the store.George had bought the blackgloves for $35 ten years ago.They were leather,softand durable.Until then,hehad worn cheaper man­made material that never lasted long.His6to buythe gloves turned out to be good,whicheven7his position on the bus,aspoorer passengers stared at him8.

      George re­entered the store.He followed the same9he had walked before,10at the bread counter,to the dairy section,to the shelf where salt and sugar wereplaced.It did not take long to be11that the gloves were notthere.His12grew heavier.“People have changed,” he13.“Years ago,if somebody14something lost,they would give it back.”

      Ye the did not give up.This time he focused on the gloves on other shoppers’ 15.Suddenly he16a ladynearby wearing a black pair of gloves.He said,“Hi!” But when the surprised lady returnedhis17,hiseyes dropped to the floor,forthe fingers of her gloves were too small for him.

     Without gloves,hehad to18his hands into his sleeves.Back home,George was19.He could notdo without gloves.George decided to buy another leather pair.But before that,he stepped into Value Mart again tosee if by any20his gloves had been returned to the lost and foundoffice.The girl looked into her drawer and took out a pair of men’s leathergloves.“Are they?”

“Yes! Mine !”George shouted with joy.

同类题4

阅读下文,回答问题

一夜能走多远

    那年我高考落榜,心情糟糕。我想出去打工,多挣点钱给父母,或许那样能弥补我对他们的愧疚。父亲说,等把地里农活儿忙完再做打算吧。

    那时候麦子已经收完,妈妈却病倒了,我家还有一块地没种上苞米。夜里落了一场透地雨,正是种苞米的良机,第二天中午,我和父亲出 发了。

    种子盛在塑料桶里,父亲刨坑我点种子,每个坑两粒种子。农历五月毒辣辣的阳光似乎要把昨夜的雨水全部收回,地面热得像蒸笼,我汗流浃背,父亲也直喘粗气。太阳落山的时候我已经筋疲力尽,口干舌燥。我们还有四垄地没种完,种子却用光了。

    我如释重负地对父亲说,正好天要黑了,咱们收工,明天再带种子来吧。父亲没说话,把锄头藏在地头的麦秸垛里,我们回家了。

    回到家,我喝了水,舒服地躺在炕上想美美地睡上一觉,却看见父亲又在弄苞米种子,我问不是明天才下种吗?现在准备有什么用?父亲笑着说,这块地今晚必须种完,否则将来会欠收。我觉得不可思议,不就差一宿吗?父亲说我们打个盹儿,一宿就过去了,但是种下去的种子不睡觉啊,同地块的苞米晚种一宿,产量差别可就大了。

    见我半信半疑,父亲指指屋檐下挂的苞米说,你看吧,这些和囤里的都是这块地的收成,前后就差一天,我拿起檐下的苞米穗与囤里的比了比,短3厘米左右!我又拿了几个比较,无一例外,檐下的苞米个头普遍偏小!

    原来,去年这片地还没有播种完,突然下了场雨,无法干活,地北头这5垄比其他地块晚种了一天。

    我被这个事实惊呆了。父亲说,大片地玉米同时吐蕊秀穗时,晚种的这几垄还未吐蕊,错过了最好的授粉期,所以收成差了许多。没想到,短短一天差到如此明显。

    一个黑夜,一个白天对于我们人类只算一个片刻,但是对于生命周期只有70多天的苞米,的确是一个不短的时间。我们看似漫长的人生不也像一粒种子般短暂吗?刚开始就落后别人一步,如不努力追赶,到后来就像檐下的苞米一样…那天傍晚,我和父亲又回到田里,把那片地全部种完,回到家时已经满天星斗。

    那年秋天我没有外出打工,而是选择了复读。经过一年的努力,我考上了一个不错的大学。一晃12年过去了,我有了稳定的工作,而与我一样落榜外出打工的几个同学,如今还辗转在烈日下的工地上辛苦地劳作,经常为讨要工钱而苦恼。

    那些装满了理想与希望的种子,短短一夜间,已经吸足了水分,早已迈开了“人生”的脚步,一旦错过,机会永不再来。