What's the oldest Tube line?

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Tags

1. #bishop
2. #paddington
3. #farringdon
4. #hammersmith
5. #world
6. #section
7. #known
8. #first
9. #railway
10. #london
11. #opened
12. #underground
13. #street
14. #between
15. #circle
16. #lines
17. #metropolitan
18. #running
19. #oldest