Normally tree rings will disappear, damage, or go missing when the tree doesn't have enough nutrients, another factor that contributes to that is drought. 
        
             
        
        
        
Answer: Option E) the products have less potential energy than the reactants
Explanation:
Though the actual graph is not displayed, but, whenever reactants occupy a position higher than the product on the graph of reaction coordinate vs time taken, it means the reactants (AB+CD) have molecules with higher energy bonds than the products AC +BD
Thus, the reaction of AB + CD to yield AC+BD will occur spontaneously with the release of energy.
 
        
             
        
        
        
The stem 
1.is responsible for the transport of food and water from the roots and leaves to the other parts of the plant
2. The stem holds the plant upright or erect
3. It also stores the nutrients 
4. It also produces new living tissues
Hope this helps!!!
        
             
        
        
        
Answer:
Each cell has a unique chemical composition
Explanation:
All the other answers are apart of the modern cell theory.
 
        
             
        
        
        
Answer:
It's changeable
Before the microscope, Linnaeus classified organisms only separated in two kingdoms, while more were introduced later. So, they were only classified in two kingdoms, they can be changed and  classified to more than  two.