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

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• 1What factor did astronomers consider when calculating the required solar mass for liquid water to exist on Earth and Mars、

  A.The young Sun lost mass at a slower rate than it currently does

  B.The young Sun was closer to the planets than it currently is

  C.The young Sun had less solar wind activity than it currently does

  D.The young Sun comprised greater amounts of helium than it currently does

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• 2Why 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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• 3Why 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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• 4Why 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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• 5What 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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