问题 选择题

海水淡化可采用膜分离技术。如图所示,对淡化膜右侧的海水加压,水分子可以透过淡化膜进入左侧淡水池,而海水中的各种离子不能通过淡化膜,从而得到淡水。对加压后右侧海水成分变化进行分析,正确的是( )

A.溶质质量增加

B.溶液质量不变

C.溶剂质量减少

D.溶质质量分数不变

答案

答案:C

解答本题的关键是审题要细,要善于找准信息:淡化膜只能让水分子通过,而离子不能通过。要明确海水是一种溶液,溶剂水以分子形式存在,而溶质以离子形式存在。对右侧海水加压,右侧溶液中的溶剂减少,溶质不变,溶液总质量减少,因此溶液中溶质质量分数变大。所以A、B、D均不正确。

单项选择题
单项选择题

Throughout the 19th century and into the 20th, citizens of the United States maintained a bias against big cities. Most lived on farms and in small towns and believed cities to be centres of (1) , crime, poverty and moral (2) Their distrust was caused, (3) , by a national ideology that (4) farming the greatest occupation and rural living (5) to urban living. This attitude (6) even as the number of urban dwellers increased and cities became an essential (7) of the national landscape. Gradually, economic reality overcame ideology. Thousands (8) the precarious (不稳定的) life on the farm for more secure and better paying jobs in the city. But when these people (9) from the countryside, they carried their fears and suspicions with them. These new urbanities, already convinced that cities were (10) with great problems, eagerly (11) the progressive reforms that promised to bring order out of the (12) of the city.

One of many reforms came (13) the area of public utilities. Water and sewerage systems were usually operated by (14) governments, but the gas and electric networks were privately owned. Reformers feared that the privately owned utility companies would (15) exorbitant (过渡的) rates for these essential services and (16) them only to people who could afford them. Some city and state governments responded by (17) the utility companies, but a number of cities began to supply these services themselves. (18) of these reforms argued that public ownership and regulation would (19) widespread access to these utilities and guarantee a (20) price.

9()

A.reallocated

B.migrated

C.replaced

D.substituted