Answer:
The correct answer is D. proliferation and differentiation.
Explanation:
Primary immune response occurs due to the first exposure of an antigen to the immune system. The primary immune response is generally delayed by many days because it takes time for B and T cells to become cloned and to proliferate and differentiate.
Then after several days of proliferation and differentiation of activated T and B cells, T cells become effector T cells and B cell becomes plasma cells which then eliminates the antigen. Memory B and T cells are also produced during this process which helps in generating a quick immune response during the second and subsequent exposure of that antigen.
So the correct answer is D. proliferation and differentiation.
 
        
             
        
        
        
Pollution can come from both natural sources and human activities depending on the type of pollutant.
<h3>What is pollution?</h3>
It is the release of substances into the environment to the extent that the well-being of plants, animals, and humans starts getting affected.
Substances that are released into the environment to the extent that they start affecting the organisms in the environment negatively are known as pollutants.
Pollutants can come from natural sources or as a result of human activities.
For example pollutants such as oxides of sulfur, methane, carbon dioxide, etc. can come from natural processes such as volcanic eruptions, activities of microbes, etc.
Pollutants such as oxides of carbon and sulfur can also be generated as a result of human activities such as the burning of coal, technological inventions, etc. 
More on pollution can be found here: brainly.com/question/23857736
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Serine, threonine, and tyrosine are most commonly phosphorylated in eukaryotes.
 
        
             
        
        
        
Answer: In an ionic bond the valence electrons are transferred from the metal only to the neighboring nonmetal, but in metallic bonding the valence electrons of each atom/ion are free to move or float around within the entire metal solid.
Explanation: