Answer:
the correct answer is b: fluid 
Explanation:
i did it and got it wrong and it gave me the correct answer
 
        
             
        
        
        
The question has incorrect option, however the question can be answered by the general explanation. On the basis of the general explanation the answer is as follows:
Answer:
The correct answer is - Serine has a small side chain that can fit in any relatively polar environment.
Explanation:
Serine is an amino acid that have a small side chain in comparison of other amino acid and can be replaced by another amino acid with very least effect on the structure and function of a particular protein as they can fit in any relatively polar environment.
Serine have hydroxyl group in their side chain. It is polar amino acid that can easily establish itself in any polar condition and cause least changes in protein structure and function.
Thus, the correct answer is - Serine has a small side chain that can fit in any relatively polar environment.
 
        
             
        
        
        
T cells
The immune response to a transplanted organ consists of both cellular (lymphocyte mediated) and humoral (antibody mediated) mechanisms. Although other cell types are also involved, the T cells are central in the rejection of grafts. The rejection reaction consists of the sensitization stage and the effector stage.
        
             
        
        
        
C. Although Alpha Centauri B is similar in size to the sun, it is much further away from earth. The sun is 8 minutes away from earth at the speed of light, while Alpha Centauri B and earth is more than 4 light years apart.