2. 外语
  3. Which of the following most logically completes the argument? A photograph of the night sky was taken with the camera shutter op

Which of the following most logically completes the argument? A photograph of the night sky was taken with the camera shutter op

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问题 Which of the following most logically completes the argument?
A photograph of the night sky was taken with the camera shutter open for an extended period. The normal motion of stars across the sky caused the images of the stars in the photograph to appear as streaks. However, one bright spot was not streaked. Even if the spot were caused, as astronomers believe, by a celestial object, that object could still have been moving across the sky during the time the shutter was open, since_________.
选项 A、the spot was not the brightest object in the photograph
B、the photograph contains many streaks that astronomers can identify as caused by noncelestial objects
C、stars in the night sky do not appear to shift position relative to each other
D、the spot could have been caused by an object that emitted a flash that lasted for only a fraction of the time that the camera shutter was open
E、if the camera shutter had not been open for an extended period, it would have recorded substantially fewer celestial objects
答案D
解析 Argument Construction
Situation In a photograph of the night sky taken with the camera shutter open for an extended period, the images of stars appeared as streaks because of the stars’ normal motion across the sky, but one bright spot was not streaked.
Reasoning What would most strongly suggest that a celestial object moving across the sky could have caused the spot? An object moving across the sky that was bright throughout the time the camera shutter was open should have appeared as a streak in the photograph, just as the stars did. But if the moving object was bright for only a very brief moment, and thus not for an extended time while the camera shutter was open, the object’s movement may not have been captured in the photograph, and thus would appear in the photograph as an unstreaked bright spot.
A The argument is not about how bright the spot was compared to other objects in the photograph.
B Streaks caused by noncelestial objects such as satellites or airplanes do not explain how only one of many celestial objects moving across the sky could have produced the unstreaked spot.
C The passage indicates that the stars were shifting position relative to the camera, not relative to one another. In any case, this observation does not help to explain how a celestial object that may not have been a star but that was moving across the sky could have produced the unstreaked spot in the photograph.
D Correct. As explained above, a moving celestial object that only produced a momentary flash of light would produce an unstreaked bright spot in the photograph.
E This may be true, given that fewer celestial objects might have moved into the camera’s range of view if the camera shutter had not been open as long. But it does not provide any evidence that a moving celestial object could have produced the unstreaked spot.
The correct answer is D.
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