Final answer:
A CASB acts as a security intermediary between cloud service users and cloud applications, enforcing an organization's security policies in the cloud.
Step-by-step explanation:
The answer to the question, which asks for a security policy enforcement software tool or service that acts as an intermediary between cloud service users and cloud applications, is b. CASB (Cloud Access Security Brokers). A CASB serves as a gatekeeper, allowing organizations to extend the reach of their security policies from their own infrastructure to the cloud. Unlike UTM (Unified Threat Management), which is more of an all-in-one security solution, or NGFW (Next-Generation Firewall), which is an advanced firewall, or DMVPN (Dynamic Multipoint Virtual Private Network), which is geared towards creating secure connections between multiple locations, CASBs are specifically designed to ensure security policies are upheld when accessing cloud services.