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Air quality in Britain has improved considerably in the last 30years. Total emissions of smoke in the air haverisen by over 85 per cent since 1950. The domestic (1)____smoking control program has been particularly important in (2)____achieving this result. London and other major cities are no (3)____longer have the dense smoke-laden “smogs” of the1950s, and in central London winter sunshine has (4)____increased about 70 per cent since 1958. (5)____ Since 1990, daily air pollution data from theBritish monitoring network has been made available (6)____to the public by the Department of the Environ-ment’s Air Quality Bulletins. These give the concen-trations of three main pollutants-ozone, nitrogendioxide and sulfur dioxide –and grade air qualityon a scale between “very weak” and “very (7)____good”. The information features in television andradio weather reports, appears in many national and (8)____local newspapers. Therefore, the data are available (9)____on a special free telephone number and on videotext systems. A comprehensive review of the issue of urbanair quality was published in January 1992. Threeindependent committees of which experts have been (10)____established to advise on different aspects of the problem, andwill set guidelines and targets for air quality. The network isalso being extended and upgraded at a cost of £10 million.
旅游团中有游客在游览时遭到蜂蛰,导游员应该怎么处理?
上颌神经属于().
Excel 2000的函数FORECAST可用于()。
说明生物膜的物质转运与调节机理。
为使片衣表面光亮,且有防潮作用,需要()
下列哪项细胞化学染色对急粒与急单的鉴别意义不大()
当两种物体接触,其间距离达到或小于2.5×10-7时,将发生电子转移,并在分界面两侧出现大小相等、极性相反的两层电荷。当两种物体迅速分离时即可能产生()。
什么是能源加工?
霍艳和丈夫来到某城市打工,由于人生地不熟,做的小本生意总是亏本,导致霍艳的丈夫性情大变,对霍艳总是看不顺眼。一天霍艳的丈夫让她帮忙买酒,她只说了一句“整天喝,生意还做不做了?”就惹来她丈夫一顿拳打脚踢。对于丈夫的变化,霍艳难以接受,萌生了离婚的念头,于是请社会工作者小萱帮忙拿主意。小萱协助霍艳分析了其个人及家庭的处境和可能的发展趋势,但并没有劝霍艳离婚或者不离婚。这体现了社会工作价值观的()。
保护接地与保护接零的保护原理是完全相同的。
说明接地保护原理。
接地保护的原理:主要是利用接地线路的()比人体()小得多,使大量的电流经接地线路流通,使人体电流甚少而起到保护作用。
接地保护是用零序分量原理构成。
保护接地与保护接零的安全原理是完全相同的。
保护接地与保护接零的安全原理是完全相同的。
什么叫保护接地和保护接零?为什么要接地和接零?
主电路的接地保护工作原理是:当DJ线圈流过的电流达到0.5A时动作,其常闭触点断开切断()线圈电路,柴油机卸载。
保护接地的原理是给人体并联一个小电阻,以保证发生故障时,()通过人体的电流和承受的电压。
主电路的接地保护工作原理是:当DJ线圈流过的电流达到0.5A时动作,其常闭触点斯开切断()线圈电路,柴油机卸载。