题干

***决定发动文化大革命的原因是(  )

A:反对林彪、江青反革命集团

B:党内出现了走资本主义道路的当权派

C:发动群众进行社会主义革命

D:他认为党和国家面临资本主义复辟的危险

上一题 下一题 0.0难度 选择题 更新时间:2012-03-31 08:13:48

答案(点此获取答案解析)

B

同类题1

化学兴趣小组的同学在实验室发现一瓶保管不当,盛有无色溶液的试剂瓶,且标签破损(如图),其残缺的标签中只剩下“Na”字样.老师告诉他们,这瓶溶液中的溶质可能是氢氧化钠、氯化钠或碳酸钠.同学们很感兴趣,决定对其成分进行探究.

【提出问题】这瓶试剂可能是什么溶液呢?

【交流讨论】根据受损标签的情况判断,这瓶试剂不可能是____(填字母).

A.酸            B.碱            C.盐

【查阅资料】碱性的Na2CO3溶液与中性的CaCl2溶液能发生复分解反应.

【作出猜想】①可能是____溶液;②可能是Na2CO3溶液;③可能是NaCl溶液.

【设计并实验】

实验

实验操作

主要实验现象

实验结论和解释

Ⅰ

取样于试管中,向其中滴加几滴无色酚酞溶液.

无色溶液变红色

该溶液不可能是____溶液.理由是____.

Ⅱ

另取样于另一支试管中,向其中滴加足量的____.

产生大量的气泡

该溶液中为碳酸钠.有关反应的化学方程式为:____.

由此,同学们得出结论:该溶液是碳酸钠溶液.

老师指出该结论不严密.理由是:氢氧化钠溶液在空气中敞开放置,发生变质,能产生与实验Ⅰ和Ⅱ相同现象.请写出氢氧化钠溶液在空气中变质的化学反应方程式____.老师指出,不需另取样,只要在实验Ⅰ后的试管中加入足量CaCl2溶液,若观察到____现象,即可说明该溶液中有氢氧化钠.

同类题5

阅读理解
    When we think of food farming we usually think of green fields in the country, outside the city. Sam Chee works on a very different type of farm, in the center of the Canadian city of Toronto. “We grow fruit, vegetables and herbs,” says Sam. “But not many people know the farm is here. You can't see it from the street. We're on top of an office building, 50 meters above the ground.”
    Rooftop farming is becoming popular in cities like Toronto, New York and London. The roofs of buildings are often just wasted space, but this space can be used for growing good fresh food, right in the middle of the city. Sam explains how it works. “We grow everything in big boxes—there are hundreds of them. We catch rainwater to water the plants when the weather is dry.”
    The rooftop farm where Sam works belongs to a restaurant called Green Garden, on the ground floor of the building. The farm produces about half the restaurant's fruit and vegetables. Sam believes that the rooftop farm is what makes Green Garden special. “We help to keep food production local. We don't need to transport this food from anywhere and that saves energy. It's better for the environment.”
    The food from the rooftop is fresher too. “When the fruit and vegetables are ripe we can pick them and use them right away. They taste better when they're really fresh,” says Sam. “I hope that there will be more rooftop farms in the city soon. It could be the farming of the future.”