Which technology enables cable operators to control access to programming services?

The correct answer is Conditional Access (CA), as this technology is specifically designed to restrict access to programming services and ensure that only authorized users can view content. Conditional Access systems work by encrypting the digital signals that carry television programming. Subscribers receive a decryption device, commonly called a smart card, which allows them to access the content they've subscribed to while blocking access to other programming that they have not paid for.

This mechanism is crucial for cable operators to manage service delivery and maintain revenue by preventing unauthorized access to premium channels or services. It ensures that subscribers can only view content they have subscribed to, thus protecting the rights of content providers and service operators.

The other options serve different purposes: Subscription Management System (SMS) is primarily concerned with handling subscriber accounts and billing efficiently rather than controlling access to content directly. Integrated Receiver/Decoder (IRD) is a device that receives and decodes the signal but does not inherently manage access rights. Digital Copy Protection (DCP) relates to protecting digital media from unauthorized copying and distribution but does not function to control subscriber access to programming services directly.