Which of the following are principles of REST architecture?

The principle of a layered system is fundamental to REST architecture because it promotes a structured and scalable approach to designing networked applications. In REST, a layered system allows different components to interact with one another without needing to be aware of the other layers. This means that client applications do not need to know whether they are communicating with the end server or an intermediate server, promoting flexibility in the architecture.

By incorporating layers, such as proxies and gateways, applications can add functionalities like load balancing and shared caching without altering the core application. This separation of concerns facilitates better organization and maintainability of applications, as each layer can focus on specific responsibilities.

In contrast, virtualization relates more to IT infrastructure and is not a principle of REST. The terms "serializable" and "cacheable" also do play important roles in networked applications—cacheability is indeed a key aspect of REST as it refers to responses that can be stored for future reuse, thus improving efficiency—but serializability does not directly pertain to REST principles. Therefore, the layered system is distinctly aligned with the foundational elements of REST architecture.