题干

某化学兴趣小组为测定Fe、Cu、Ag三种金属的活动性顺序,选用下列各组试剂,你认为不可行的是(  )


A:Cu、FeCl2溶液,AgNO3溶液

B:Cu、Ag、FeSO4溶液

C:Fe、Ag、CuSO4溶液

D:Fe、Cu、稀硫酸,AgNO3溶液

上一题 下一题 0.0难度 选择题 更新时间:2019-01-16 05:47:56

答案(点此获取答案解析)

B

同类题3

阅读理解

    Have you ever wondered when dogs first became “man's best friend” and the world's favourite pet? If you have then you're not alone. When and where dogs first began living side-side with humans are questions that have stirred hot debate among scientists. There are a few hard facts that all agree on. These include that dogs were once wolves and they were the first animal to be domesticated(驯养) by humans. They came into lives some 15000 years ago, before the dawn of agriculture.

    Beyond that, there is little agreement. The earliest bones found that are unquestionable dogs and not wolves date from 14,000 years ago. However, 30,000-year-old skulls have been discovered in France and Belgium that are not pure wolf and some scientists think could be dogs.

    With such puzzling evidence, many scientists are now turning to DNA to find out when and where dogs were first domesticated. In one research project, tens of thousands of blood samples have been taken from street dogs around the world. The plan is to compare them with those of wolves. It's even possible to analyse DNA from ancient bones. Tiny pieces of the 30,000-year-old skulls mentioned earlier are currently being studied, and another DNA study has already shown that ancient dogs preserved in the Alaskan ice-fields evolved from Asian wolves, not American ones.

    Indeed, the ancient DNA may turn out to be more informative than the DNA of living dogs. Because dogs have accompanied humans around the world for thousands of years, their current distribution may tell us very little of their origins. This is why different groups of scientists believe that dogs variously originated in eastern Asia, Mongolia, Siberia, Europe or Africa.

    But why were the animals domesticated in the first place? The most recent theory is that dogs domesticated themselves, initially living in and around our ancient villages to eat any food thrown out. Today, this is a way of life still shared by three -quarters of a billion unowned dogs worldwide.

同类题4

阅读下面的文章,完成小题。

秋天的怀念

史铁生

       ①双腿瘫痪以后,我的脾气变得暴怒无常。望着望着天上北归的雁阵,我会突然把我面前的玻璃砸碎;听着听着李谷一甜美的歌声,我会猛地把手边的东西摔向四周的墙壁。母亲悄悄地躲出去,在我看不见的地方偷偷地听着我的动静。当一切恢复沉寂,她又悄悄地进来,眼边红红的,看着我。“听说北海的花都开了,我推着你去走走。”她总是这么说,母亲喜欢花,可自从我的腿瘫痪后,她侍弄的那些花都死了。“不,我不去!”我狠命地锤打这两条可怕的腿。喊着:“我活着有什么劲!”母亲过来抓住我的手,忍住哭声说:“咱娘儿俩在一块儿,好好儿活,好好儿活……”

       ②可我却一直都不知道,她的病已经到了那步田地,后来妹妹告诉我,她常常肝疼得整宿整宿翻来覆去睡不了觉。

       ③那天我又独自在屋里,看着窗外的树叶“唰唰啦啦”地飘落。母亲进来了,在窗前:“北海的菊花开了,我推着你去看看吧。”她憔悴的脸上现出央求般的神色。“什么时候?”“你要是愿意,就明天?”她说,我的回答已经让她喜出望外了。“好吧,就明天。”我说。她高兴得一会儿坐下,一会儿站起:“那就赶紧准备准备。”“哎呀,烦不烦?几步路,有什么好准备的!”她也笑了,坐在我身边,絮絮叨叨地说:“看完菊花,咱们就去‘仿膳’,你小时候就爱吃那儿的豌豆黄儿。还记得那回我带你去北海吗?你偏说那杨树花是毛毛虫,跑着,一脚踩一个……”她忽然不说了。对于“跑”和“踩”一类的字儿,她比我还敏感。她又悄悄地出去了。

       ④她出去了,就再也没回来。

       ⑤领导们把她抬上车时,她还在大口大口地吐着鲜血。我没想她已经病成那样,看着三轮车远去,也决没想到那竟是永远的诀别。

       ⑥邻居家的小伙子背着我去看她的时候,她正艰难地呼吸着,像她那一生艰难的生活。别人告诉我,她昏迷前的最后一句话是:“我那个有病的儿子和那个还未成年的女儿……”

       ⑦又是秋天,妹妹推我去北海看菊花。黄色的花淡雅,白色的花高洁,紫红色的花热烈而深沉,泼泼洒洒,秋风中正开得烂漫。我懂得母亲没有说完的话。妹妹也懂。我俩在一块儿,要好好儿活……