What is the role of WindowsBase.dll portion of managed code in Managed layer of Windows Presentation Foundation (WPF)?

This portion holds the top level WPF elements like Windows, panels, controls, styles, etc.

It implements the end-user presentation features.

It provides a managed wrapper for MIL and implements the core services for WPF such as UI Element and visual from.

It holds basic elements to be reused outside the WPF environment like Dispatcher objects and Dependency objects.

None of the above