What is the relationship between Ashtead Group 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.

Risers Ashtead Group (LSE: AHT.L - news ) (AHT) 1,080.00p +1.98% Land Securities Group (LAND) 1,250.00p +1.46% Hammerson (HMSO) 634.00p +1.20% St James's Place (STJ) 927.00p +1.09% Pearson (PSON) 1,228.00p +1.07% British Land Company (BLND) 809.50p +1.06% Randgold Resources Ltd. (RRS) 4,248.00p +0.95% Barratt Developments (LSE: BDEV.L - news ) (BDEV) 641.00p +0.94% London Stock Exchange Group (LSE) 2,445.00p +0.74% Intu Properties (INTU) 315.10p +0.51% Fallers Vodafone Group (NasdaqGS: VOD - news ) (VOD) 230.35p -2.35% Standard Chartered (STAN) 1,029.00p -2.33% Morrison (Wm) Supermarkets (MRW) 176.40p -2.11% Sainsbury (J) (SBRY) 261.20p -1.95% Rolls-Royce Holdings (RR.)

Answer: headquarters_location