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问题 选择题

下表中，对陈述I、II的正确性及其有无因果关系的判断都正确的是

选项陈述I陈述II判断
A铁是地壳中含量最高的金属元素铁是人类最早使用的金属材料I对；II对；有
B常温下铁与稀硫酸反应生成氢气高温下氢气能还原氧化铁生成铁I对；II对；无
C铁属于过渡金属元素铁和铁的某些化合物可以用作催化剂I错；II对；无
D铁在空气中表面生成致密氧化膜可用铁罐储存运输浓硫酸、浓硝酸I对；II对；有

答案

答案：B

铝是地壳中含量最高的金属元素，铜是人类最早使用的金属材料，选项A不正确；过渡元素常用作催化剂，因此选项C中有因果关系，C不正确；铁在空气中表面不能生成致密氧化膜，所以选项D不正确，答案选B。

选择题

如图所示，使一薄钢条的下端固定，现分别用不同的力去推它，F1＝F3＝F4>F2，使其发生a、b、c、d各图中所示的形变，能说明力的作用效果与力的方向有关的两张图是

[ ]

A．a和b

B．b和d

C．a和d

D．a和c

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填空题

The central problem of economics is to satisfy the people’s and nation’s wants. The problem we are faced with is that our (1) , here identified as money, are (2) . The only way we can resolve our (3) is to make choices. After looking at our resources, we must examine our list of (4) and identify the things we need (5) , those we can postpone, and (6) we cannot afford. As individuals, we face the central problem involved in economics — deciding just how to allocate our limited resources to provide ourselves with the greatest (7) of our wants.
Nations face the same problem. As a country’s population (8) , the need for more goods and services grows (9) . Resources necessary to production may increase, but there are (10) enough resources to satisfy the total desires of a (11) . Whether the budget meeting is taking place in the family living-room, in the conference room of the corporation (12) of directors, or in the chamber of the House of Representatives in Washington, the basic problem still exists. We need to find (13) of allocating limited resources in order to satisfy unlimited wants.
A short time ago, economists divided goods into two categories, free and economic. The former, like air and water, were in (14) abundance that economists had no concern about (15) of scarcity and what to do about it. Today many of these "free goods" are in (16) very expensive to use. Pollution has made clean air and water expensive for producers who have to filter their waste products, for consumers who ultimately pay for the producers’ extra costs, and (17) tax-payers who pay for the government’s involvement in cleaning the environment.
In the 1990s, almost all goods are (18) . Only by effort and money can they be (19) in the form people wish.
Meeting the needs of people and the demands from resources available leads to the basic activity of production. In trying to (20) unlimited wants from limited economic goods, production leads to new problems in economics.
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