问题 选择题

某同学对下列四个实验方案的设计中不合理的是(  )

选项ABCD
实验

目的

除去氢氧化钠溶液中少量的碳酸钠清洗铁制品

表面的铁锈

鉴别氯化钠

溶液和稀盐酸

检验生石灰是否变质
方案加稀硫酸加适量稀盐酸加锌粒滴加稀盐酸,通入澄清石灰水

A.选A

B.选B

C.选C

D.选D

答案

A、硫酸既会与氢氧化钠反应,也会与碳酸钠反应,除去杂质时,也会除去主要物质,故A错误;

B、盐酸会与氧化铁反应而将铁锈溶解,故B正确;

C、盐酸会与锌粒反应,加入锌粒,会产生气泡,说明有盐酸;无气泡,说明是氯化钠荣格.故C正确;

D、生石灰会变质成碳酸钙,加入盐酸如果有气泡,说明发生了变质,无气泡,说明不变质,故D正确;

故选A.

单项选择题

In the absence of optimism, we are left with nothing but critics, naysayers, and prophets of doom. When a nation expects the worst from its people and institutions, and its experts focus exclusively on faults, hope dies. Too many people spend too much tie looking down rather than up, finding fault with their country’s political institutions, economic system, educational establishment, religious organizations, and—worst of all—with each other.

Faultfinding expends so much negative energy that nothing is left over for positive action. It takes courage and strength to solve the genuine problems that afflict every society. Sure, there well always be things that need fixing. But the question is, do you want to spend your time and energy tearing things down or building them up

The staging of a Broadway show could illustrate my point. Let’s say a new production is about to open. A playwright has polished the script, investor have put up the money, and the theater has been rented. A director has been chosen, actors have been auditioned and selected, and the cast has been rehearsing for weeks. Set, lighting, and sound engineers have been hard at work. By the time opening night arrives, nearly a hundred people have labored tirelessly—all working long hours to make magic for their audience.

On opening night, four or five critics sit in the audience. If they pan it, the play will probably close in a matter of days or weeks. If they praise it, the production could go on for a long and successful run. In the end, success or failure might hinge on the opinion of a single person—someone who might be in a bad mood on opening night! What’s wrong with this scene In one sense, nothing. Critics have a legitimate role. The problem arises when we make critics our heroes or put them in control of our fate. When we empower the critic more than the playwright, something is wrong. It is much easier to criticize than to create. When we revere the critics of society, we eventually become a society of critics, and when that happens, there is no room left for constructive optimism.

What might be the ultimate result of a biased bitter criticism().

A. More rebellion.

B. More creativity.

C. Less initiative.

D. Less destruction.

判断题