What is the relationship between Vodafone 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 London firm advised last week that " m ore of our European businesses are returning to growth ," and a 1.5% decline in organic service revenues during April-June indicates the vast strides made over the past year -- Vodafone saw European revenues droop 4.7% during the 12 months to March.

Answer: headquarters_location