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在“探究光反射的规律”时，让一束光EO贴着纸板射到平面镜上，在纸板上会看到反射光线OF．将纸板NOF沿ON向后折，此时在NOF面上看不到反射光线，如图乙所示，此实验说明_____________________________________．在图甲中，如果让光线逆着OF的方向射向镜面，会看到反射光线沿着OE方向射出，这表明_____________________________

甲乙

答案

反射光线、入射光线和法线都在同一平面内；在反射现象中，光路是可逆的

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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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单项选择题 A1/A2型题

女患者，阴部干涩，灼热瘙痒，五心烦热，头晕目眩，耳鸣，腰酸。舌红少苔，脉细数无力。治宜（）

A.清热解毒，除湿止带

B.行气祛湿止带

C.滋肾降火，调补肝肾

D.清热利湿，杀虫止痒

E.健脾益气，升阳除湿
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