A hypersensitive reaction to a specific antigen in the environment is a(n) _ALLERGY_.
        
             
        
        
        
Earth’s thin, rocky outer layer is its crust. A small example is like a crust on a piece of bread. :) 
C is your answer 
        
                    
             
        
        
        
Answer:
Explanation:
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The answer is
If it is a leap year, then February has 29 days.
<span>A conditional statement uses a pattern of ‘if’ followed
by ‘then’. The obvious cause must be stated first followed by the outcome. ‘If
and only if’ is an example of a biconditional statement. </span>