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问题 选择题

在下列溶液中放入锌片，一段时间后将锌片取出，溶液质量增加的是（　　）

A．氯化镁溶液

B．氯化钠溶液

C．硫酸铜溶液

D．硝酸银溶液

答案

A、由于镁的活动性要比锌更强，所以把锌片放入氯化镁溶液中不会发生反应，溶液的质量不变．故A不符合题意；

B、由于钠的活动性要比锌更强，所以把锌片放入氯化钠溶液中不会发生反应，溶液的质量不变．故B不符合题意；

C、把锌片放入硫酸铜溶液中，锌能把铜置换出来，由反应时的质量关系可知，每65份质量的锌可置换出63.5份质量的铜，因此溶液的质量会增加，C符合题意；

D、把锌片放入硝酸银溶液中，锌能把银置换出来，由反应时的质量关系可知，每65份质量的锌可置换出216份质量的银，因此溶液的质量会减轻，D不符合题意．

故选C．

填空题

What is distance learning It means that you study on your own, at home or wherever suits you. Recently, the world famous Open University in the United Kingdom has designed a new style of distance learning, which is called (1) . The phrase "Open Learning" means you study (2) . You read course material, work on course activities, and write (3) . The word "Supported" means you have help (4) , the student services staff at regional centres, and centralized areas such as (5) . You can also contact other students through tutorials and (6) , the University’s online conferencing system, and events and clubs organized by (7) . Most distance learning courses use printed paper materials. They also include some (8) materials such as a CD, DVD or video. Many courses have a web site and an (9) . You’ll need access to a computer (10) to make use of these. The Open University can help its students buy a computer and (11) the cost of accessing the Internet.

With most distance learning courses, no (12) are required to study. of course, you have to be aged 18 when your course starts but there is no (13) . Currently the Open University has around (14) undergraduate and more than 30,000 postgraduate students, of which 10,000 have (15) . Nearly all students are studying (16) . About 70 per cent of undergraduate students are in (17) . More than 50,000 students (18) by their employers for their studies. Most distance learning courses (19) . Some of them are even available in other parts of the world. With over 25,000 of its students living outside the UK, the Open University is the (20) that offers distance learning throughout the world.

16（）
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单项选择题

活动隔墙安装表面平整度允许偏差（）

A、5mm

B、4mm

C、3mm

D、2mm
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