NPPE professional practice principles emphasize that responsibility for engineering/geoscience work rests with the licensed professional who applies professional judgment, signs/seals work, and relies on the results.
Commercial software is a tool; it does not transfer accountability to the vendor or to a disclaimer. The professional must ensure the software is suitable for the task, inputs and assumptions are correct, limitations are understood, and outputs are validated using checks (hand calculations, benchmark problems, sensitivity analyses, or alternative methods). Even if the employer owns the project and carries organizational liability, the professional remains professionally accountable for the technical validity of results they use and for decisions based on those results. Therefore, the responsibility for accuracy and validity lies with the professional (C), not the software developer (B), not merely the employer (A), and not in any disclaimer (D).