What is the relationship between 'Vodafone' and 'London' in the context of the input sentence.
Options: original broadcaster, legal form, headquarters location, product/material produced

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.
headquarters location