请从下 * * 个代数式中任选两个构造一个分式,并化简该分式. (1)a2-1,ab-

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问题:

请从下 * * 个代数式中任选两个构造一个分式,并化简该分式.

(1)a2-1,ab-b,b+ab

(2)x2-4xy+4y2,x2-4y2,x-2y.

考点:分式的定义分式的基本性质
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.

Valuing water

Human beings use a little less than half the water available worldwide. Yet shortages and droughts(干旱) are causing starvation and poverty in some areas, and industrial and agricultural by-products are polluting water supplies. Since the world’s population is expected to double in the next 51 years, many experts think we are on the edge of a widespread water crisis.

But that doesn’t have to be the result. Water shortages do not have to trouble the world—if we start valuing water more than we have in the past. Just as we began to value petrol more after the 1970s oil crisis, today we must start looking at water from a fresh economic view. We can no longer afford to consider water a nearly free resource of which we can use as much as we like in any way we want.

Instead, for all uses except the demand of the poor, governments should price water to reflect its real value. This means charging a fee for the water itself as well as for the supply costs.

Governments should also protect this source by providing water in more economically and environmentally sound ways. For example, often the cheapest way to provide irrigation(灌溉) water in the dry places is through small-scale projects, such as gathering rainfall in depressions(凹地) and pumping it to nearby cropland.

No matter what steps governments take to provide water more efficiently, they must change their ways to use water. Rather than control hundreds or even thousands of local, regional agencies that watch water use, countries should set up central authorities to manage water policy.

65. What is the real cause of the potential water crisis?

A. Only half of the world’s water can be used.

B. The world population is increasing faster and faster.

C. Half of the world’s resources have been seriously polluted.

D. Human beings have not placed sufficient value on water resources.

66.We can conclude from the passage that the water problem______.

A. is already serious in certain parts of the world

B. has been exaggerated by some experts in the field

C. poses a challenge to the technology of building reservoirs

D. is underestimated by government organizations at different levels

67.According to the author, the water price should______.

A. be reduced to the minimum

B. stimulate domestic demand

C. equal its real value

D. take into account the occurrences of droughts.

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长期运行的电动机,对其轴承应两年进行一次换油。

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中国近年来出口农副产品结构统计表

年份出口农副产品总额(万元)以出口农副产品总额为100计
初级深加工
198571.399.810.2
198789.589.710.3
1989150.684.315.7
1991340.956.643.4
1993698.449.850.2
1995711.647.652.4

1991年我国农副产品出口总额为多少万元?()

A.170.6

B.340.9

C.3409

D.150.6

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黄仁宇在《中国大历史》中指出:“中国从公元前一直到20世纪,中央政府能向每个农民直接征税,是世界上唯一的国家。”能做到这一点的根本原因在于()

A.编户制度

B.三省六部制

C.中央集权制

D.行省制

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提高消费服务社会化需要的条件包括()

A.消费者收入水平提高

B.消费者自我保护能力提高

C.时间价值的升值

D.社会服务行业的规模发展

E.消费者权益保护意识提高

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