In Large Soup Pot, Bring Stock To A Boil. Add Chicken And Reduce Heat To A Simmer. In Small Pan, Melt Butter Over Medium Heat. Add Onions, Celery And Carrots. Saute Until Celery Is Tender. Add Vegetables To The Pot And Simmer For 30 Minutes. Add Salt And Pepper And Rice. Simmer For 5 Minutes. Serve Garnished With Parsley.