A new building has been added to the enterprise campus network， providing client access for desktop PCs， laptops， and IP phones for employees and guests. During verification， only a few laptops using  wireless are reported to have problems， while other desktops， IP phones， and most other wireless laptops are fully operational. Additional information received about the problem indicates that， while the problematic wireless laptops cannot reach internal corporate websites， they can reach the Internet.  Where should troubleshooting about this connectivity issue be focused？（）

• A、client network configuration
• B、VLAN mapping
• C、routing protocols
• D、first-hop redundancy protocol