What is the relationship between 'Safaricom' and 'Nairobi' in the context of the input sentence.
Options: headquarters location, developer, founded by, location of formation

With over 12 million subscribers accessing the internet through its network, Safaricom pioneered its LTE Advanced (4G) proposition in December 2014, launching the most advanced version of the 4G system for mobile networks in Nairobi and Mombasa.
headquarters location