题干

通过观察化学实验现象,分析归纳出正确的结论,是学习化学科学最基本的技能之一.下列由实验现象得出正确结论的是(   )

选项

实验现象

结论

A

把相同大小的一块铝和镁分别投入相同浓度的NaOH溶液中:铝溶解有气泡放出,而镁没有任何变化

由此得出:铝的金属性比镁强

B

取一块铝箔,用酒精灯点燃:铝箔只熔化成液体而没有脱落

由此得出:铝不易燃烧

C

向氯化铵溶液中投入一铝片:铝片上产生大量气泡

由此得出:该气体是氨气

D

向氯化铝溶液中逐滴滴加NaOH溶液至过量:先产生白色沉淀,后沉淀逐渐溶解,最后沉淀完全消失

由此得出:氢氧化铝能溶于强碱溶液

A:A  

B:B  

C:C  

D:D

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答案(点此获取答案解析)

D

同类题3

阅读理解

    We've considered several ways of paying to cut in line: hiring line standers, buying tickets from scalpers (票贩子), or purchasing line-cutting privileges directly from, say, an airline or an amusement park. Each of these deals replaces the morals of the queue (waiting your turn) with the morals of the market (paying a price for faster service).

    Markets and queues—paying and waiting—are two different ways of allocating things, and each is appropriate to different activities. The morals of the queue, “First come, first served, have an egalitarian (平等主义的) appeal. They tell us to ignore privilege, power, and deep pockets.

    The principle seems right on playgrounds and at bus stops. But the morals of the queue do not govern all occasions. If I put my house up for sale, I have no duty to accept the first offer that comes along, simply because it's the first. Selling my house and waiting for a bus are different activities, properly governed by different standards.

    Sometimes standards change, and it is unclear which principle should apply. Think of the recorded message you hear, played over and over, as you wait on hold when calling your bank: “Your call will be answered in the order in which it was received.” This is essential for the morals of the queue. It's as if the company is trying to ease our impatience with fairness.

    But don't take the recorded message too seriously. Today, some people's calls are answered faster than others. Call center technology enables companies to “score” incoming calls and to give faster service to those that come from rich places. You might call this telephonic queue jumping.

    Of course, markets and queues are not the only ways of allocating things. Some goods we distribute by merit, others by need, still others by chance. However, the tendency of markets to replace queues, and other non-market ways of allocating goods is so common in modern life that we scarcely notice it anymore. It is striking that most of the paid queue-jumping schemes we've considered—at airports and amusement parks, in call centers, doctors' offices, and national parks—are recent developments, scarcely imaginable three decades ago. The disappearance of the queues in these places may seem an unusual concern, but these are not the only places that markets have entered.

同类题4

 阅读,完成文后习题

井绳

    通向月亮的路并不是美国航天局首先发现的。在他们之前,在古代,我们的先人就已经发现了接近月亮的最佳方式。

    方法很简单。只需要一眼井,一汪清水,一根井绳,一颗虔诚的心。

    面对水井的时候,要让自己燥热、混乱、凶狠的心静下来,不要怀着总想征服什么的冲动,内心安静一些,清澈一些。低下你高贵的头,夸下你高贵的身子,你就会看见,从水里,从岁月深处,一轮洁净明亮的初月正向你升起,并渐渐地走向你,走进你的生活。

    美国航天局用了很大的劲爬上了月亮,只抓了几块冰冷的石头让人类看,让人类扫兴,让人类的神话和童话破灭,让孩子们面对冰冷的石头不再做美丽的梦。他们让人类离月亮越来越远,离石头越来越近。

    我父亲不知道人类的宇航船在天上折腾些什么,他心目中的月亮仍然是古时候的那个月亮。那是神秘的月亮,是嫦娥的月亮,吴刚的月亮。没读过诗的父亲也知道,李白打捞的就是水里的那个月亮。

    父亲几乎天天都要和月亮会面。他一生都在打捞水中的那个月亮。你见过我父亲在月夜里挑水的情景吗?

    他抬头望一眼天上的月亮,微笑着低下头来,就看见水井里等待出水的月亮。他弯下腰伸出手,就把那月亮打捞上来。

    两个水桶里,盛着两个月亮,一前一后。乍一看,是父亲挑着月亮;仔细看,是两个月亮抬着父亲,一闪一闪地在地上行走。

    通向月亮的路有多长?据美国航天局说,是30万公里。走了30万公里,他们到达了一块冰冷的石头。我丈量了父亲用过的井绳,全长3米。父亲通过这3米的距离,打捞起完整的月亮和美丽的月光。

    审美是需要保持距离的。取消距离,美国得到一块冰冷的石头;谦卑地怀着敬畏守着一段距离,我父亲满身披着圣洁的月光。

    我发现,美国是一个会折腾的技术员,我父亲是一个与天地精神往来的美学家。

    我记着父亲那根井绳,3米之下,就能接触到月亮;3米之上,到处是伸手可掬的白银般的月光。