DLP, or data loss prevention, and CASB, or cloud access security broker, are the solutions that when installed and configured would best meet the CSO's requirements. DLP is a technology that monitors and prevents unauthorized or accidental data leakage or exfiltration from an organization's network or devices.
DLP can use document attributes, such as metadata, keywords, or fingerprints, to identify and classify sensitive data and enforce policies on how they can be accessed, transferred, or shared. CASB is a technology that acts as a proxy or intermediary between an organization's cloud services and its users. CASB can provide visibility, compliance, threat protection, and data security for cloud-based applications and data. CASB can also prevent on-site staff from accessing personal SaaS solutions that are not authorized by the organization.
References: [CompTIA CASP+ Study Guide, Second Edition, pages 281-282 and 424-425]