What is the relationship between 'Nomura Securities' and 'Nomura Holdings' in the context of the input sentence.
Options: parent organization, platform, owned by, headquarters location

He previously held senior roles at Nomura Securities Co, the brokerage unit of Nomura Holdings Inc. After he left Nomura, Saito served as CEO of the Industrial Revitalization Corporation of Japan, a now-defunct state-backed turnaround fund that invested in troubled companies.
parent organization