_______ there no plants, what _____ to oxygen in the air?
A.Had… would have happened
B.Were … would have happened
C.Were … would happen
D.Should … would have happened
A.Had… would have happened
B.Were … would have happened
C.Were … would happen
D.Should … would have happened
What kind of engine did the Hyper-X use?
A.A jet engine that carries its own oxygen supply.
B.A jet engine that uses no oxygen.
C.A scramjet engine that doesn't carry its own oxygen supply.
D.A rocket engine that carries its own oxygen supply.
A.photothermal
B.photoelectric
C.photosynthesis
D.--
32 What kind of engine did the Hyper-X use?
A A jet engine that carries its own oxygen supply.
B A jet engine that uses no oxygen.
C A scramjet engine that doesn't carry its own oxygen supply.
D A rocket engine that carries its own oxygen supply.
What will continue to be ______ it is today--next in importance to oxygen?
A.how
B.which
C.what
D.as
A.Water
B.Hydrogen
C.Carbon dioxide
D.Nitrogen
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