Environmental Science
In a volume of air near the earth's surface, ____ occupies 78 percent and ____ nearly 21 percent.

Hydrogen, helium
Hydrogen, oxygen
Nitrogen, oxygen
Nitrogen, water vapor
Oxygen, hydrogen

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Environmental Science
Definition of ecosystem is

The community of organisms together with the environment in which they live
The part of the earth and its atmosphere which inhibits living organisms
The abiotic component of a habitat
A community of organisms interacting with one another

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