Which two national capitals lie on the Río de la Plata estuary?

Which two airlines flew the supersonic Concorde until it was retired in 2003? Which bird does Papa promise to buy in the lullaby "Hush, Little Baby"? Which two animals support the shield on Australia's coat of arms? Jesus nicknamed which pair of brothers "Boanerges," or "Sons of Thunder"? Which Caribbean island is an overseas department of France? In 1997, which teenage country star's version of "How Do I Live" spent a then-record 69 weeks on the Billboard Hot 100? Which Virginia college, chartered in 1693, is the second-oldest institution of higher education in the U.S.? Which 1931 standard became a 1968 hit for Cass Elliot of the Mamas & the Papas?