Environmental Science
A food web is

The tropic (feeding) levels that can be observed in an ecosystem
The set of prey species that are consumed by animals in an ecosystem
A set of interconnected food chains, illustrating the tropic relationships among species
Like a food chain

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Environmental Science
The aurora is produced by:

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

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