Necessary because it keeps heat in and keeps the planet at the right temperature for life. 
It can harm the planet if more pollution occurs and the greenhouse gas effect traps too much heat and causes global warming
        
             
        
        
        
Answer: The peripheral nervous system.
Explanation: We have two parts to our nervous system. The central nervous system and the peripheral nervous system. The CNS is located in the brain and spinal cord the PNS is the nerves and ganglia outside of those. 
 
        
                    
             
        
        
        
For the given situation above, I'm afraid I cannot answer your question since a pedigree chart isn't provided along with the question. You can resubmit your question together with the chart and we'll analyze it. Thank you for posting though. Here is what pedigree analysis is about.
Scientists have devised an approach, called pedigree analysis<span>, to study the inheritance of genes in humans. Pedigree analysis is also useful when studying any population when progeny data from several generations is limited. Pedigree analysis is also useful when studying species with a long generation time.</span>
        
                    
             
        
        
        
Answer:
            According to Dr. Ray Schiling (member of the American Academy of Anti-aging medicine) about 1.5 million people suffer from peanut allergies. The seeds of peanut (<em>Arachis hypogea</em>) contain an array of allergens that can induce the production of IgE specific antibodies predisposed individuals. Ara1 and Ara2 are most common seed storage protein that cause allergy. Other allergen proteins such as Ara3 to Ara 17 have also been identified that cause allergy.  
Entry of peanut allergen into body
When peanut allergens enter the body of an individuals it leads to development of different symptoms like itchy skin, tingling sensation, nausea, runny nose and anaphylaxis.  
Allergic response
There are two subsets of T-cells Th1 and Th2. Both invoke different response to allergens. Th1 direct a non-allergic response while Th2 direct allergic response ranging from releasing of histamine to anaphylactic response. The presence of IL-12 cytokines direct a Th1 based, nonspecific response.  
Mechanism of allergic response (interaction between helper T cell and B cell)
Step 1.  
            When allergen enter to body they are encountered by B cells. Immunoglobulin receptors on the surface of B cells recognize antigen (Peanut allergens) and get attached, which are then internalized and processed. Within B cells the fragments of antigens combine with HLA class 2 proteins.  
Step 2
              HLA class 2 with antigen fragments (peanut allergens) then display on the surface of B cells.
Step 3
             Receptors on the surface of helper T cells recognizes the complex of HLA class 2 and antigen fragments (peanut allergen) and is activated to produce cytokines, which activate the B cells.  
Step 4
              B cell is activated by cytokines and begins clonal expansion. Some of the progeny become anti-body producing plasma cells while other become memory B cells.  
 
        
             
        
        
        
Answer:
option C is the right answer