What is the relationship between Western Digital and SanDisk 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.

Hard-disk drive maker Western Digital Corp will buy SanDisk Corp in a $19 billion that will greatly increase its ability to make flash memory storage chips used in smartphones and tablets.

Answer: subsidiary