Your answer would be D.
A harmful mutation is what it seems to be- it is a mutation which harms an organism's chances at survival.
Therefore, the correct answer would be D.
From this logic, we can also deduct it cannot be A. It cannot be B either, or most likely won't be - a phenotype is the entire characteristic of an organism, its behavior, traits, etc. Phenotypes are also influenced by the environment, which a genetic mutation has nothing to do with. Finally, it wouldn't be C. A genetic mutation of one organism would not change the environment of the organism, only the organism who's genetics it is.
Good luck!
