ANS: C

Oxygen in itself is a very reactive element. It binds quickly to other materials. Remember, free oxygen
only became abundant in our atmosphere when photosynthetic organisms began producing more.
Thus, if there is a large amount of free oxygen, then there is something present that is replacing it in
the atmosphere. This is likely to be a life-form of some sort. Information can be found in the section
Are There Other Ocean Worlds


ANS: C
A supernova is a shattering expansion in which there is an explosive release of energy. This explosion,
lasting only thirty seconds, can demolish a star. Information can be found in the section Stars and
Seas.

Environmental & Atmospheric Sciences

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