What is the relationship between Parcelforce and Royal Mail 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.

The continuing downturn in letter deliveries pushed revenue in the company's UKPIL business - which operates in the UK collecting and delivering parcels and letters through the Royal Mail Core Network and Parcelforce Worldwide - down 2pc.
parent_organization