Is It Theoretically Possible to Alter the Genes of Any

Is it theoretically possible to alter the genes of any living species, and if so, why don't we?

A) No. Human genes work differently from genes of other species so science does not yet have the technology to engineer humans.
B) No. Every species genes work a bit differently so not every gene that works in one species will work in another.
C) Yes, but the process is difficult, expensive, and ethically questionable.
D) Yes, but the process is difficult, expensive, and not that many people or corporations are actually working on doing it.
E) Yes, but doing so is generally against the law.