Environmental Science
The aurora is produced by:

Fast-moving charged particles colliding with air molecules
Reflections of sunlight by polar ice fields
Scattering of sunlight in the upper atmosphere
Burning oxygen caused by the intense sunlight at high altitude
The combination of molecular and atomic oxygen to form ozone

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Environmental Science
Biogas is composed of

carbon dioxide, nitrogen and hydrogen
methane, carbon dioxide, nitrogen and sulphur
ethane, carbon dioxide, nitrogen and hydrogen
methane, carbon dioxide, nitrogen and hydrogen

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