World record progression 100 metres backstroke

Columns: Time | Swimmer | Date | Place
52.71 | Mark Tewksbury | March 16 , 1991 | Bonn , Germany | 52.58 | Mark Tewksbury | March 29 , 1991 | Sheffield , Great Britain | 52.52 | Mark Tewksbury | February 20 , 1992 | Winnipeg , Canada | 52.50 | Mark Tewksbury | February 22 , 1992 | Winnipeg , Canada | 51.43 | Jeff Rouse | April 12 , 1993 | Sheffield , Great Britain | 51.28 | Lenny Krayzelburg | February 5 , 2000 | Berlin , Germany | 50.75 | Neil Walker | March 19 , 2000 | Athens , Greece

Example questions:
What nationality is the Men 's World record progression 100 metres backstroke swimmer with a time of 52.71 seconds ? | How many Olympic gold medals did the Men 's World record progression 100 metres backstroke swimmer with a time of 51.28 seconds win ? | How many times has the Men 's World record progression 100 metres backstroke swimmer with the shortest time been named world champion ?

Answers:
Canadian | four | twice