Answer !
a harmful mutation

(a)increases the organism’s ability to reproduce
(b)alters the phenotype of the organism
(c)changes the environment of the organism
(d)reduces the organism’s chance for survival

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!