What could ultimately be linked to the present absence of water ...

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What could ultimately be linked to the present absence of water on Mars?
  a. The large decrease in carbon dioxide
  b. The proximity to the sun
  c. The lack of free oxygen in the atmosphere
  d. The lack of outgassing from the interior of the planet
  e. Excess carbon dioxide

Question 2

High levels of ____ could indicate life on other planets.
  a. free nitrogen
  b. carbon dioxide
  c. free oxygen
  d. methane
  e. ozone

[trampas]

Answer to Question 1

a

Answer to Question 2

c

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