The correct answer is:  [D]:  "receives venous blood from the lower extremity" .
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Answer:
Independent Variable: Time each plant is exposed to daylight.
Dependent Variable: Hours of exposure
Constant Variables: Species of plant, location of each plant, amount of soil, amount of water, and tempurature.
Explanation:
Independent variable: the variable that stays the same.
Dependent: the measurement that is used to measure the independent variable. 
Constant: the variables that stay the same in a experiment.
 
        
             
        
        
        
Answer:
a. 40%
Explanation:
up to 40% increasing the light intensity increases the oxygen production. Beyond 40% there is no effect.
I hope this helps :)
 
        
             
        
        
        
Do you have any answer choices