What is the relationship between Babcock International 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.

The chairmen of FTSE 100 engineering giant Babcock International (LSE: BAB.L - news ) , British Land (LSE: BLND.L - news ) and the AA have put their names to an open letter from Heathrow chairman Sir Nigel Rudd urging ministers to support expansion of the west London airport.

Answer: headquarters_location