What is the relationship between Halliburton and HOUSTON 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.

HOUSTON (Reuters) - Business is so tough for oilfield giants Schlumberger NV and Halliburton Co that they have come up with a new sales pitch for crude producers halting work in the worst downturn in years.

Answer: headquarters_location