What is the relationship between GroupM and advertising 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.

That contract is estimated to be worth $15 million to $30 million, and has resulted in 30 blue chip advertising clients in the GroupM portfolio using premium YouTube ads this year.

Answer: industry