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A light that has a light period shorter than its dark period

题目
单选题
A light that has a light period shorter than its dark period is described as（）.
A

flashing

B

pulsating

C

occulting

D

alternating

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相似问题和答案

第1题：

Which of the following is NOT mentioned(提到)in this passage?

A. The problems that light pollution has caused.

B. The reason why humans use too much light.

C. The ways that light pollution can be reduced.

D. The reason why fewer stars can be seen than before.


正确答案：B

第2题：

The literature of a period () its values and tastes.

A、reflects

B、talks

C、engages

D、distorts


参考答案：A

第3题：

Thomas is afraid of the dark, () he sleeps with a light on in his room.

A、therefore

B、because

C、however

D、then


参考答案：A

第4题：

The symbol which appears beside a light on a chart reads Gp Fl R (2) 10 sec 160 ft 19M. Which characteristic describes the light?

A.It is visible 10 miles

B.Its distinguishing number is 19M

C.It has a radar reflector

D.None of the above


正确答案：D

第5题：

What’S the main idea of the passage7

A．Laser light treatment of heart disease should take the place of the traditional operatlon．

B．Laser light treatment has been proved better and more effective than the traditional operation．

C．More advanced technology should be encouraged to try on．

D．Laser light treatment of heart disease still needs’more research．


正确答案：D
通读全文，特别是最后一段后半部分，可知正确答案应是D项。

第6题：

6． It s getting dark，please _________ the light．

A． turn off

B． turn on

C． turn down

D． turn up


正确答案：B

第7题：

Which term means “the profit that a company has obtained from selling its products or services in a particular period of time, in relation to its sales for the period”?

A、Annual income

B、operation profit

C、return on sales

D、net profit


参考答案：C

第8题：

What is the fifth paragraph mainly about?

A. Why people become short-sighted.

B. Why natural light has a special chemical.

C. Why playing outside is good for one’s eyesight.

D. Why daylight is much brighter than indoor light.


正确答案：C

第9题：

When a buoy is in position only during a certain period of the year，where may the dates when the buoy is in position be found?

A.Light List

B.Notice to Mariners

C.On the chart

D.Coast Pilot


正确答案：A

第10题：

共用题干
Learn about Light
1 .Ancient civilizations were amazed by the existence of light for thousands of years. The Greek philosophers believed that light was made up of countless,tiny particles that enter the human eye and create what we call vision. However,Empedocles and a Dutch scientist named Christian Huygens believed that light was like a wave. According to them,light spread out and travelled like a straight line. This theory was accepted during the 19th century.
2 .In 1905,Albert Einstein published a research paper in which he explained what is re-ferred to as the photoelectric effect. This theory explains that particles make up light.The particles Einstein was referring to are weightless bundles（束）of electromagnetic（电磁）energy called photons（光子）.Today,scientists agree that light has a dual（二重）nature一it is part particle and part wave. It is a form of energy that allows us to see things around us.
3 .Things that give off light are known as sources of light. During the day,the primary source of light is the sun. Other sources of light include stars,flames,flashlights,street lamps and glowing gases in glass tube.
4 .When we draw the way light travels we always use straight lines. This is because nor-mally light rays travel in a straight line. However,there are some instances that can change the path and even the nature of light. They are reflection,absorption,interference（干扰）, etc.
5 .Physicists have attempted to measure the speed of light since the early times. In 1849, Hippolyte Fizeau conducted an experiment by directing a beam of light to a mirror located kilometers away and placed a rotating cogwheel（旋转齿轮）between the beam and the mirror. From the rate of rotation of the wheel,number of wheel's teeth and distance of the mirror,he was able to calculate that the speed of light is 313 million meters per second. In a vacuum（真空）,however,the speed of light is 299,792,458 meters per second. This is about a million times faster than the speed of an airplane.

Paragraph 5______
A: How Is the Nature of Light Explained Today?
B: What Are Sources of Light?
C: How Did Physicists Measure the Speed of Light?
D: How Does Light Travel?
E: How Did People Think of Light Years Ago?
F: What Causes a Shadow?

答案：C
解析：
该概括大意与完成句子所选的阅读材料为记述文，段落主题相对于论述文而言较松散，因此记述文中的段落大意往往需要考生根据自己的理解而归纳概括出来。解答概括大意题的技巧往往派不上用场。第二段主要讲述现代科学家认同了爱因斯坦的光电效应理论。因此可以判断A选项“当今人们如何解释光的性质”正确。
第三段第一句“Things that give off light are known as sources of light.”就点明主旨，发光的物体是光源。所以B选项“什么是光源？”正确。
第四段主要讲述光传播的问题，所以D选项“光是如何传播的”正确。
第五段的关键字是speed of light，光速。所以C选项“物理学家如何测量光的速度”正确。
题干意为“人们可以看见物体是因为光……。“从第二段最后一句可知，人们看见物体是因为光是一种能量。所以F项a form of energy正确的。
题干意为“星星、火焰、手电筒都是……的例子。”第三段“Other sources of light include stars , flames , flashlights...”说明，这些都是光源的例子。所以A选项sourcesof light是正确的。
题干意为“某些情况下，如反射和吸收可以改变……。”第四段中“there are some instances that can change the path and even the nature of light.They are reflection,ab-sorption , interference , etc.”这说明有一些情况可以改变光的路径。所以C选项the path of light是正确的。
题干意为“Hippolyte Fizeau做了一个刚试……的实验。”文中最后一段 “Hippolyte Fizeau conducted an experiment by directing a beam of light to a mirror...he was able to calculate that the speed of light...”可知Hippolyte Fizeau通过实验计算出了光速。所以B选项是正确的。

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