题干

氢氧化钙的溶解度随温度升高而减小.要想把一瓶接近饱和的石灰水变成饱和,具体措施有:①加入氢氧化钙;②升高温度;③降低温度;④加入水;⑤蒸发水.其中措施正确的是(   )

A:①②④

B:①③④

C:①③⑤

D:①②⑤

上一题 下一题 0.0难度 选择题 更新时间:2018-11-23 09:31:52

答案(点此获取答案解析)

D

同类题1

阅读下文,回答问题

祸从天降,谁为真凶

陈祺

      ①2010年8月7日,一场突如其来的灾难降临甘肃省舟曲县,昔日秀美的山中小城顿时满目疮痍,许多同胞不幸罹难。罪魁祸首,就是泥石流。那么,泥石流到底是怎么发生的呢?

      ②泥石流是暴雨、洪水将含有沙石且松软的土质山体经饱和稀释后形成的洪流。相对于普通洪水,泥石流含有大量泥沙石块等固体碎屑物,最高体积含量可达80%,因而具有更大的破坏力。它往往发生在山区等沟谷深壑、地形险峻的地区。

      ③舟曲县城所在的白龙江地区地势起伏较大,山谷地势高差达1000-2000米,而且舟曲正好处于两山之间的峡谷地带,这给泥石流汇集和流动形成了天然的地理条件。舟曲位于龙门山地震活动带北缘,又临近天水地震活动带。由于历史上的几次大地震,舟曲附近的地质构造岩性松软、破碎,风化程度严重,堆积物很多。此外,灾害发生之前持续的干旱造成附近山体干缩,加大了岩石间、山体间的缝隙,使原本已十分松散的岩体、山体互相之间更加没有黏性。

      ④这些地质条件给舟曲埋下了安全隐患,但如果没有力量去推动这些松散物质的话,泥石流依然不会发生。暴雨就是推动泥石流的“手”。

      ⑤处于黄土高坡上的舟曲县原本是一个干旱的地区,多年的平均年降水量不到200毫米。有历史记载的暴雨近百年来只发生过2次,分别是1973年7月 12日的57.2毫米暴雨和1994年8月8日的63.3毫米暴雨。本次舟曲泥石流暴发当晚,该地区在短短40分钟内突降97毫米的大暴雨。大量的水浸透沟床中的固体堆积物质,使其稳定性降低。饱含水分的固体堆积物在自身重力作用下发生运动,形成了泥石流。作为生命之源的水成了这场灾难的导火索和帮凶。

      ⑥如果说强降雨是“导火索”的话,山体风化、水土流失则是“火药”,而人类活动担当了“催化剂”的角色。

      ⑦20世纪50年代,舟曲县森林覆盖面大,生态环境平衡,有“陇上江南”之称。然而之后的半个多世纪,舟曲的森林覆盖率从67%锐减到20%。森林的过度砍伐导致舟曲水土流失严重,山体风化,土地裸露,一旦遇到狂风暴雨,泥石流就容易形成并沿着山谷倾泻而下。另外,近10年来,舟曲县获批的大小水电站有55座。修建水电站要炸山辟地,会令岩体变得松动,植被遭到破坏,制造了大量的松散物质。更有甚者,舟曲矿产资源丰富,开矿遗留的废弃土石处理不当,使松散碎屑物质量大增。这样,在自然状态下需数十、数百乃至上千年才能聚集起来的松散碎屑物质量,现在几年内便达到了。桶里装满了“火药”,自然一点就炸。

      ⑧由此可见,舟曲泥石流的形成不完全是因为天灾,人为因素也促进了泥石流的发生发展,扩大了它的规模,加重了危害程度。在经济发展中应该重视环保,只有真正贯彻落实可持续发展,才能避免悲剧重演。

(选自《中学科技》2010年10期,有改动)

同类题2

阅读理解

    Cycling or even walking in city areas can be a little dangerous, thanks to the fact that one is sharing the road with vehicles that are increasingly getting larger and heavier. A recent study proves that of the 1.27million people that die in road traffic crashes each year, about half are walkers, motorcyclists and cyclists. Now there may be a solution that could provide at least some help to protect this helpless group---an airbag!

    If you are worried that this safety measure will involve you taking around a heavy package or worse still, wrapping yourself inside an ugly plastic bag, the bag is fitted not on the human, but on the outside of the vehicle. And, while there are several versions of the idea in the works, the one most recently unveiled by Dutch car company TNO, seems to be the most advanced and ready to go into production.

    In the works since 2011, the airbag covers only the lower part of the windshield. This will provide the much needed buffer(缓冲)between the person's head and the pane of glass he/she would otherwise meet.

    The chain of events leading to an airbag cause are quite simple---A camera fitted beneath the rear-view mirror monitors the vehicle's closeness to a walker or cyclist. Any contact with either one of them sets off the sensors in the car's bumper and quickly blows up the airbag. In addition to that the sensors also set off the car's automatic brake, reducing the chances if an even worse injury.

    In tests conducted using a model, the success of not getting injured after being hit by a car travelling at about 40km/h was about 50-50! While not perfect, it will still result in reducing the number of deaths by a huge amount.

    With TNO ready to license its technology to car makers and many more companies trying to develop similar concepts, we would not be surprised if outer airbags become a standard feature in every car pretty soon.