Of all Barry H．Landau's anecdotes about his friendships with presidential dogs,perhaps the best is the one about the time the Clinton White House called to postpone his play-date with Buddy．

Yes,Landau is both human and an adult,a 60-year-old author,presidential historian,former White House protocol officer and memorabilia collector．But so enamored is he of dogs,and so well connected to a succession of presidents,that he had an appointment for a South Lawn romp one day with Buddy,Bill Clinton's Labrador retriever(拉布拉多犬).

Logistics got in the way,though,and hence Clinton secretary Betty Currie's apologetic voice mail left at the Smithsonian Institution,where Landau was doing research:"I'm sorry,but we'll have to reschedule Mr．Landau's play-date with Buddy."

Not surprisingly,this is a happy week for Landau,with the new Obama family dog,Bo,joining a White House tradition that dates to George Washington．It's one that Landau feels is invaluable to a presidency.

"Having a dog just humanizes a president,"he says．"It completes the picture．It's something people can relate to."

And Landau has related to the best of them．He's known about 25 White House dogs since the Eisenhower administration．Among the presidential-pooch memorabilia in his Manhattan apartment are matching orange inaugural dog coats worn by LBJ's twin beagles(小猎犬),Him and Her,and a photo of Landau kissing Clipper,JFK's German shepherd.

Who was the first president to have a dog in the White House?

• A.Bill Clinton
• B.John Kennedy
• C.Dwight Eisenhower
• D.George Washington