What is the relationship between Safaricom and Nairobi 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.

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.

Answer: headquarters_location