Someone steals the King Lion's ring.One of the following four is the thief.Now,only one of them tells the truth .Who is the thief?Choose the correct one from the following choices.( )
1.duck:The cow is the thief.
2.lion:I stay at home reading with the cow,never out.
3.cow:I see the little duck steal the ring.
4.bird:Little duck and I stole the ring.