What is the relationship between Betfair and London in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

1,076.50p -0.32% G4S (Amsterdam: GF6.AS - news ) (GFS (Taiwan OTC: 6026.TWO - news ) ) 254.70p -0.27% Smiths Group (Other OTC: SMGKF - news ) (SMIN) 1,199.00p -0.17% FTSE 250 - Risers CLS Holdings (LSE: CLI.L - news ) (CLI) 1,884.00p +2.67% Daejan Holdings (LSE: DJAN.L - news ) (DJAN) 6,550.00p +2.26% Foxtons Group (LSE: FOXT.L - news ) (FOXT) 242.60p +2.15% Allied Minds (Other OTC: ALLWF - news ) (ALM) 490.00p +2.08% Betfair Group (LSE: BET.L - news ) (BET) 2,851.00p +1.79% Pets at Home Group (PETS) 278.20p +1.76% Entertainment One Limited (Other OTC: ENTMF - news ) (ETO) 331.70p +1.75% Derwent London (LSE: DLN.L - news ) (DLN) 3,756.00p +1.65% Jupiter Fund Management (JUP) 458.70p +1.59% Zoopla Property Group (WI) (ZPLA) 280.50p +1.59% FTSE 250 - Fallers Cranswick (CWK) 1,630.00p -1.57% Wizz Air Holdings (WIZZ) 1,856.00p -1.38% Wood Group (John) (WG.)

Answer: headquarters_location