Answer:
Shape, Size, Height, Type of Food
Explanation:
The color is the variable and the type of hummingbird can't be controlled.
One species is nocturnal, and the other species is not.
http://quizlet.com/51808791/biology-1407-ch-24-flash-cards/
The answer to this question would be Fermentation. This is a process that releases energy when oxygen is insufficient.
