Which definition best describes the staging plan development service component within the design phase？ Select exactly 1 answer（s） from the following：（）。

• A、providing a step-by-step plan that details the installation and service-commission tasks required in order to create a controlled-implementation environment that emulates a customer network
• B、assessing the ability of site facilities to accommodate proposed infrastructure changes
• C、developing and executing proof-of-concept tests， validating high-level infrastructure design， and identifying any design enhancements
• D、improving the network management system and the performance and functionality of infrastructure operations