Which of the following is the PRIMARY mechanism used to limit the range of objects available to a given subject within different execution domains?

Process isolation enforces separate execution domains for each process by assigning distinct virtual address spaces and privilege rings, ensuring that a subject can only access the objects within its own domain. The operating system uses hardware memory protection (MMU) and privilege levels to prevent one process from reading or writing another process's memory or resources. This directly limits the range of objects available to a given subject based on its execution context and trust level.

Data hiding and abstraction are software design principles used in object-oriented programming to conceal implementation details, not the primary OS-level mechanism for enforcing execution domain boundaries between subjects.

Discrete layering and APIs define structured interfaces and communication pathways between system layers, but they are architectural design concepts rather than the enforcement mechanism that actively restricts object access within execution domains.

A Virtual Private Network (VPN) is a network security technology that encrypts and tunnels traffic between endpoints over a public network, and has no role in managing execution domain boundaries or object access control within an operating system.