protected string AddPassiveSuffix(string suffix1, string suffix2, string suffix3, string prefix, TxtWord root,
                                          string stem)
        {
            Transition transition;

            switch (root.VerbType())
            {
            case "F4PW":     //"nDH"
            case "F4PW-NO-REF":
                transition = new Transition(suffix1);
                break;

            case "F5PR-NO-REF":     //"DH"
            case "F5PL-NO-REF":
                transition = new Transition(suffix2);
                break;

            default:     //"HlDH"
                transition = new Transition(suffix3);
                break;
            }

            return(prefix + transition.MakeTransition(root, stem));
        }