THIS IS LUNA, a two-year-old labrador/retriever mix, with Erin Scranton, a Falls Church resident who raised and trained her to be an assistance dog for Canine Companions for Independence, a national nonprofit that trains and provides assistance dogs. Luna recently moved to New York to live with Stephen Yaciuk, who has a hearing disability. In New York, Luna will alert Stephen to sounds, like telphone ringing, doorbells or even smoke alarms.