Which pair of shows are the longest-running dramas in TV history?

• "Law & Order" & "Gunsmoke"
  Both "Law and Order" and "Gunsmoke" ran for an astonishing 20 TV seasons, making them the longest-lived TV dramas ever.
• "Gunsmoke" and "Bonanza"
  Both "Law and Order" and "Gunsmoke" ran for an astonishing 20 TV seasons, making them the longest-lived TV dramas ever.
• "ER" and "Dallas"
  Both "Law and Order" and "Gunsmoke" ran for an astonishing 20 TV seasons, making them the longest-lived TV dramas ever.