B, Gases. The gases create an insulation around the planet so it keeps in heat from heat sources.
        
             
        
        
        
Unicellular organisms consist of one cell only that performs all vital functions including metabolism, excretion, and reproduction. They are responsible for obtaining nutrients, producing energy, and making proteins.
        
             
        
        
        
The answer is A.) carbon dioxide, water, oxygen, nitrogen, and hydrogen
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A. Venus
B. Asteroid
C. Comet
D. Uranus
        
                    
             
        
        
        
Definite article is used before a noun (person place or thing) to indicate that the identity of the noun is known to the reader. 
indefinite article is used before a noun that is general or when its identity is not known.