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【单选题】
防晒霜之所以能有效地减轻紫外线对人体的伤害，是因为它所含的有效成分的分子中含有π键，这些有效成分的分子中的π电子可在吸收紫外线后被激发，从而阻挡部分紫外线对皮肤的伤害。下列物质中没有防晒效果的是 [     ]
A.
氨基苯甲酸
B.
羟基丙酮
C.
肉桂酸（C 6 H 5 -CH=CH-COOH）
D.
酒精
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【单选题】Economic models
A.
are essentially different from those used in other sciences.
B.
always use graphs.
C.
simplify reality.
D.
include all relevant facts.
查看完整题目与答案
【单选题】We can infer that current virtual reality devices ______.
A.
still need improving to create a perfect virtual world
B.
are already perfect to create a virtual world
C.
are unable to create a virtual world
D.
are harmful to users of virtual reality
查看完整题目与答案
【单选题】Which of the following statements about economic models is correct?
A.
Economic models are built to mirror reality exactly.
B.
Economic models are useful, but they should not be used for the purpose of improving public policies.
C.
Because economic models omit many details, they allow us to see what is truly important.
D.
Economic models seldom incorporate equations or diagrams.
查看完整题目与答案
【单选题】Traditional economic models found it hard to explain the phenomenon of .
A.
search frictions
B.
unemployment
C.
labor as commodity
D.
wage falls
查看完整题目与答案
【单选题】Economic models
A.
are people who act out the behavior of firms and households so that economists can study this behavior.
B.
are usually detailed replications of reality.
C.
incorporate simplifying assumptions that often contradict reality, but also help economists better understand reality.
D.
are useful to researchers but not to teachers because economic models omit many details of the real-world economy.
查看完整题目与答案
【单选题】Economic models
A.
cannot be useful if they are based on false assumptions.
B.
were once thought to be useful, but that is no longer true.
C.
must incorporate all aspects of the economy if those models are to be useful.
D.
can be useful, even if they are not particularly realistic.
查看完整题目与答案
【多选题】数据模型的结构有( )。
A.
结构化数据
B.
非结构化数据
C.
半结构化数据
D.
完全结构化数据
查看完整题目与答案
【单选题】电缆转弯时弯曲半径应符合规定,屏蔽4对对绞电缆的弯曲半径至少为电缆外径的( )。
A.
4倍
B.
6倍
C.
8倍
D.
10倍
查看完整题目与答案
【单选题】Economic models
A.
are not useful because they omit many real-world details.
B.
are usually composed of diagrams and equations.
C.
are useful because they do not omit any real-world details.
D.
contribute very little to economists’ understanding of the real world.
查看完整题目与答案
【单选题】Some child ren stated that they used their unsupervised free time to perfec t their athletic skills, such as playing basketball
A.
GemmaGemma spent hours trying to perfect her technique spent hours trying to perfect her technique
B.
The treaty is far from perfect, but it is clearly the way forward.
C.
In English, the perfect is formed with "have" and the past participle of the verb.
查看完整题目与答案
相关题目：
【单选题】Economic models
A.
are essentially different from those used in other sciences.
B.
always use graphs.
C.
simplify reality.
D.
include all relevant facts.
查看完整题目与答案
【单选题】We can infer that current virtual reality devices ______.
A.
still need improving to create a perfect virtual world
B.
are already perfect to create a virtual world
C.
are unable to create a virtual world
D.
are harmful to users of virtual reality
查看完整题目与答案
【单选题】Which of the following statements about economic models is correct?
A.
Economic models are built to mirror reality exactly.
B.
Economic models are useful, but they should not be used for the purpose of improving public policies.
C.
Because economic models omit many details, they allow us to see what is truly important.
D.
Economic models seldom incorporate equations or diagrams.
查看完整题目与答案
【单选题】Traditional economic models found it hard to explain the phenomenon of .
A.
search frictions
B.
unemployment
C.
labor as commodity
D.
wage falls
查看完整题目与答案
【单选题】Economic models
A.
are people who act out the behavior of firms and households so that economists can study this behavior.
B.
are usually detailed replications of reality.
C.
incorporate simplifying assumptions that often contradict reality, but also help economists better understand reality.
D.
are useful to researchers but not to teachers because economic models omit many details of the real-world economy.
查看完整题目与答案
【单选题】Economic models
A.
cannot be useful if they are based on false assumptions.
B.
were once thought to be useful, but that is no longer true.
C.
must incorporate all aspects of the economy if those models are to be useful.
D.
can be useful, even if they are not particularly realistic.
查看完整题目与答案
【多选题】数据模型的结构有( )。
A.
结构化数据
B.
非结构化数据
C.
半结构化数据
D.
完全结构化数据
查看完整题目与答案
【单选题】电缆转弯时弯曲半径应符合规定,屏蔽4对对绞电缆的弯曲半径至少为电缆外径的( )。
A.
4倍
B.
6倍
C.
8倍
D.
10倍
查看完整题目与答案
【单选题】Economic models
A.
are not useful because they omit many real-world details.
B.
are usually composed of diagrams and equations.
C.
are useful because they do not omit any real-world details.
D.
contribute very little to economists’ understanding of the real world.
查看完整题目与答案
【单选题】Some child ren stated that they used their unsupervised free time to perfec t their athletic skills, such as playing basketball
A.
GemmaGemma spent hours trying to perfect her technique spent hours trying to perfect her technique
B.
The treaty is far from perfect, but it is clearly the way forward.
C.
In English, the perfect is formed with "have" and the past participle of the verb.
查看完整题目与答案