What factor did astronomers consider when calculating the required solar mass for liquid water to exist on Earth and Mars、

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• 1Why does the professor mention the solar wind、

  A.To explain a way the Sun is losing mass

  B.To point out that it was less intense billions of years ago

  C.To suggest a reason for early climate differences between Earth and Mars

  D.To explain the importance of solving the faint-young-Sun paradox

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• 2Why did the greenhouse-gas solution fail to explain the early presence of liquid water on Earth and Mars、 [Choose two answers]

  A.The types of gases that were present in their atmospheres could not have caused temperatures to rise

  B.There was insufficient carbon dioxide in their atmospheres to produce a greenhouse effect.

  C.Solar radiation would have destroyed the ammonia in their atmospheres.

  D.Clouds of ammonia would have lowered temperatures by blocking out sunlight.

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• 3Why is geological evidence of liquid water on Earth and Mars three to four billion years ago problematic、

  A.It suggests that the solar system is younger than it could possibly be.

  B.It suggests that the young Sun was less bright than it is today.

  C.It challenges the prevailing model of star formation.

  D.It contradicts theories about the beginning of the universe

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• 4What is the main propose of the lecture、

  A.To compare solutions to the greenhouse-gas problem

  B.To examine methods used to study star formation in other solar systems

  C.To discuss evidence for liquid water on young Earth and Mars

  D.To discuss attempts to solve a puzzle related to the Sun

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• 5Why does the professor say this、

  A.He does not approve of all the aspects of the shows.

  B.He does not think the events can be easily defined.

  C.He does not consider the shows to be authentic Dada.

  D.He does not know enough about the events to categorize them.

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• 6What is the professor's attitude about the bright-young-Sun solution、

  A.He is surprised that it is not more widely accepted

  B.He feels that it raises too many unanswerable questions

  C.He is confident that future research will determine whether it is true.

  D.He expects that other possible solutions to the paradox will be proposed.

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