As an experienced technician, you are responsible for Technical Support in your company. You ask one of the trainees to document the layers of an existing CIS network. Which three statements best characterize this process? （）(Choose three.)

• A、It provides reliable input for verifying network consistency.
• B、It requires a network audit to support some upgrade decisions.
• C、It requires a network audit to support any network restructuring.
• D、It begins with gathering organizational input that may be inaccurate.