Correct Answer: A, C, DWhen maintaining a Citrix Virtual Apps and Desktops environment with Citrix App Layering, the Citrix Engineer needs to consider the following: Application and Platform Layers are directly tied to the operating system layer on which they were created, meaning each different OS Layer needs its own respective Application and Platform Layers. Before an OS version or layer can be deleted from the Citrix App Layering Management console, it must first not be in use by an existing template, ensuring no dependencies remain. The engineer needs a unique layer for each OS build created to maintain proper separation and functionality; this includes having different OS Layers for different builds of the same OS type, such as separate layers for 32-bit and 64-bit versions. These considerations are crucial for effective image management and ensuring compatibility across various operating systems in the infrastructure.