ViewContainerRef in Angular is used to manage the DOM elements where dynamic components are inserted. It provides a reference to the container where you can dynamically add or remove components. This is useful for scenarios where you need to render components based on user interactions or application logic. The other options are not the primary purpose of ViewContainerRef.

To restrict loading of modules based on user roles in a lazy-loaded scenario, you should implement the CanLoad guard. It allows you to check conditions before the module is loaded, ensuring that only authorized users can access certain parts of the application.

To send a GET request using HttpClient, you would use the get() method. This method is used to perform HTTP GET requests to retrieve data from a specified URL.

When a service is provided in the 'root' of an Angular application, it becomes a singleton. This means there's only one instance of the service for the entire application. Services provided in a module are scoped to that module, creating a new instance for each module that imports it.

In Angular's routing, the CanLoad guard determines whether a module can be lazily loaded. This guard is used to protect routes that are loaded on-demand, typically through lazy loading, and it checks conditions before allowing the module to load. CanActivate is used to determine if a route can be activated, but it doesn't control lazy loading.

In RxJS, the forkJoin operator is used when you need to combine multiple Observables and wait for all of them to complete before emitting a result. It will emit an array of the last values from each Observable when they have all completed.

To implement an undo feature in NgRx, you would leverage "Time-travel debugging." This feature allows you to step backward and forward through the state changes, effectively enabling undo and redo functionality in your application.

The routerLink directive can be bound to an array, allowing you to pass parameters to the route. This is useful for passing dynamic data to routes, such as route IDs or other contextual information. While the routerLink can also be bound to other types of data, like arrays or queries, it's primarily used for passing parameters.

When two modules provide the same service and are imported into a third module in Angular, the service from the 'first' module will be used. Angular's dependency injection system follows a hierarchical order for providing services. The first module providing the service takes precedence over the second module, and so on. This ensures that the service is consistent and predictable in its usage.

In Angular, you use the createComponent() method provided by TestBed to create an instance of a component for testing. This method allows you to set up and configure the component in a controlled testing environment.