What is the relationship between Apple Inc and iPhone 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.

Barron's said investors in GoPro are "skittish" about the company's ability to ward off competition from Apple Inc (APPL.O), which has upgraded the camera on its iPhone to produce more high resolution video.

Answer: product_or_material_produced