题干

向溶液中通入CO2一定不会产生沉淀的是(   )

A:Ca(OH)2 (aq)

B:Ca(NO3)2(aq)

C:Na2CO3(aq)

D:NaAlO2(aq)

上一题 下一题 0.0难度 选择题 更新时间:2012-08-08 03:15:46

答案(点此获取答案解析)

B

同类题4

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,并在答题卡上将该项涂黑。选项中有两项为多余选项。

    All around the world, people are working hard to make their cities safer and more pleasant for pedestrians (行人). Cities havepainted crosswalks on their streets, made streets narrower, put in traffic lights and speed bumps (减速带) and madeplans to help more kids walk or bike to school.

    Many people have learned from a man from Brisbane, Australia,named David Engwicht. His book Reclaiming Our Cities and Towns has a simplemessage____. Kids playedthere, and neighbors stopped there to talk.

    But now, streets are just for cars and trucks. People stay inside to get away from the noise and dangerous traffic, and we lose contact with our neighbors____.  People needto take back their streets. Engwicht travels around the world, helping people think differently about pedestrians, streets, and neighborhoods.____. He has workedin neighborhoods from Honolulu to Scotland.

    While Engwicht was writing his book, he learned how neighbors in the city of Delft, in the Netherlands, stopped dangerous traffic on their street. They put old couches, tables, and planters in the street.____. When the police arrived, they saw how these illegal actions made the streets safer. Soon city officials started planning ways to make cars slow down, and“calm”thetraffic.

    Engwicht says we should think about streets as our “outdoor living room”.____

    In the future, streets will be safe places for children again,and our neighbors will become our friends.

a. Cars and pedestrians crowded the street.

b. Calming the traffic is just the beginning.

c. Cars could still pass, but they had to drive slowly.

d. He says that in the past, streets belonged to everybody.

e. It's hard to take measures to solve the traffic problems.

f. Besides his books and articles, he gives many speeches.

g..  Engwicht says that we should use streets for more than just transportation.

同类题5

阅读下面的文字,完成下面小题。

材料一:

    进入二十一世纪以来,我国城镇化发展进入加速阶段,社会经济中的城市群体化现象越来越显著,城市群的作用也越来越大。中国传统的省域经济,正在向城市群经济转变。城市群是中国未来经济发展格局中最具潜力的核心地区。

    区域经济发展的质量是由区域内各城市、各要素的融合程度决定的。融合是指在高水平上的城市协调关系和要素合理配置,是通过集聚和扩散实现的。世界三大著名的大湾区城市群,起步于得天独厚的区位条件,港口、公路和机场等基础设施优先发展;同时,产业、资本和市场集聚。

    通过对长三角、粤港澳、京津冀、长江中游、成渝、海西、山东半岛七个城市群的人口、土地、经济概况进行分析,可以发现:近五年人口净流入最多的城市群为长三角城市群,人口吸引力比较高,尤其是“211”、“985”名校聚集的上海、杭州、南京等城市名列前茅;人口涌入最少的则是海西城市群,即使核心城市福州和厦门,城市竞争力也稍弱。从土地占比和地区生产总值占比来看,粤港澳的地均产出最高,是第二名长三角城市群地均产值的二倍之多;地均产出最低的城市群为成渝城市群,仅占粤港澳城市群的1/7。

材料二:

    京津冀城市群的城镇化水平为62.72%,城镇体系趋于完善中,基础设施较为完善,基本判别其现在处于趋于成熟阶段;长三角城市群城镇化水平为68.47%,城镇密度区域较稳定,同时基础设施水平也是所有城市群中最完善的,属于内涵式增长阶段,基本判别其处于成熟发展阶段;而粤港澳城市群城镇化水平高达84.41%,区域内部相对较为平衡,城市空间组织扩散高于集聚作用,城镇密度也处于相对合理的稳定状态,基本判断其处于成熟发展阶段;长江中游城市群、成渝城市群、海峡西岸城市群、山东半岛城市群由于城镇化率比较低,还处于集聚作用为主、扩散作用为辅的外延式发展阶段,处于快速发育阶段。

表1:城市群不同发展阶段特征

指标

雏形发育阶段

快速发育阶段

趋于成熟阶段

成熟发展阶段

城镇化率

30%左右

30%—50%

50%—70%

70%以上

城镇体系

不完善、城镇密度低

较为完善、城镇密度较高

完善,城镇密度继续提高

完善,城镇密度区域稳定

空间结构

松散、基础设施不完善

较紧密、基础设施较完善

紧密、基础设施完善

最紧密、基础设施相当完善

空间作用

集聚作用占绝对优势

集聚为主,扩散为辅

集聚与扩散相对平衡

扩散作用略占优势

城市分工

分工系统还未形成

分工体系开始形成

分工体系相对合理

分工体系完善

增长路径

外延式增长

外延式为主、内涵式为辅

内涵式为主、外延式为辅

内涵式增长

材料三:表2:七大城市群空间组织结构

城市群名称

城市首位度

经济首位度

核心城市集中度

城市群空间结构

长三角城市群

2.28

1.73

56.6%

多中心结构,相对较均衡

粤港澳城市群

1.19

1.03

57.2%

双中心,相对均衡

京津冀城市群

1.4

1.39

64.2%

三中心,不均衡

长江中游城市群

1.43

1.28

40.4%

三中心,不均衡

海西城市群

1.94

1.62

24.4%

双中心,不均衡

成渝城市群

2.06

1.46

60.4%

双中心,不均衡

山东半岛城市群

1.28

1.52

26.5%

双中心,不均衡

注:城市首位度:城市发展要素在最大城市的集中程度。

经济首位度越高,说明该城市在这个地区的经济实力、地位越高。

材料四:

①增长极开发模式  ②点轴式开发模式    ③点轴群开发模式    ④网络开发模式