What is the oldest Tube line?

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Tags

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