What is the relationship between British Airways 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.

MONTREAL, July 29 (Reuters) - A British Airways flight from Las Vegas to London made an emergency landing in Montreal early on Wednesday due to concern that a bomb threat had been made, an airport spokesman said.

Answer: headquarters_location