The conversation between madame valmonde and desiree gives an example of Foreshadowing; situational irony;
Considering this Quote;
Madame Valmonde "shuddered at the first sight of it.....It was a sad lokking place.......The roof came down steep and black like a cowl, reaching out beyond the wide galleries that encircled the yellow stuccoed house. Big, solemn oaks grew close to it, and their thick-leaved, far-reaching branches shadowed it like a pall."
The imagery in this quote reveals the darkness of a place that is ironically called a shelter, and Madame Valmonde mentions the "pall" that is cast over the house , that being a term related to death. 
        
                    
             
        
        
        
The answer is a. Nitrogen
        
             
        
        
        
Keystone predators effect their habitat by keeping the population of animals down.
        
             
        
        
        
This process is mitosis. mitotic cell division is how they grow.