D most intense and longest duration is the answer
        
             
        
        
        
The formula used can be found in Quora.com (population*average height)/Earth's circumference), gives the result of the number of the human chain. 
If the average height of an American is 1.77m and the US population is  326, 292, 068 (June 2, 2017) and if everyone is already an adult. 
US population 326, 292, 068
Average height according to study 
is estimated as the same as arm span  <span>1.77
</span>Earth circumference in meters: <span>40,075,000
</span>
<span>
(</span>326, 292, 068 people * 1.77m) / 40,075,000m = 14.411 times
        
             
        
        
        
I believe it would be Heat Radiation
        
                    
             
        
        
        
Answer: 
Stem tubers grow from rhizomes or runners that swell from storing nutrients while root tubers propagate from roots that are modified to store nutrients and get too large and produce a new plant. Examples of stem tubers are potatoes and yams and examples of root tubers are sweet potatoes and dahlias.
Is this the answer your looking for?
        
                    
             
        
        
        
Because you might have just done something different with the experiment and messed up someway during the test