People often says that a dog isman'sbest friend.Over thousands ofyears,man has taughthisdogstodomanykindsofworkbesidesguarding thehome.Forexample,sheepdo gs arefamousfortheir ability tocontrolaflockof hundredsof sheep. Dogshavebeenusedtoaiddisabledpeopleforcenturies.Aguidedogcanleaditsblindowner.Nowadays,dogscanbetaughttoturnonlightswitches,openrefrigeratordoors anddial thetelephonefortheirdisabledowners.Forthemajorityofpeople,however,dogs are simplypetsandfriendsforbothyoung andoldmembersof thefamily.