Answer: option A - Constant in genotype and phenotype 
Explanation:
Pan mixia is a situation in which an individual is just as likely to mate with another randomly chosen individual as any other in the population
In a situation as described in the question, sexual reproduction is limited to organisms of the same habitat, thus the genetic variation is reduced to the BAREST MINIMUM. 
This results in Constancy in genotype and phenotype 
 
        
             
        
        
        
It's like editing over what's already written. it's the process of reading something and marking for any error. (: Usually deemed more helpful when you let two completely different people proof read the same paper to get a better result! 
Good luck, rockstar! (: I wish you the best and hope you pass!