Definition: The third planet from the sun.
Example: You are sitting on it, and it's not a chair.

earth

Explanation:

because it's the third planet from the sun

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explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.