After working all night and successfully configuring a Cisco router for the TestKing network you save your changes on the startup config, reboot the router, and go out for a cigarette. When you return, none of your changes are active and the router boots to the initial configuration mode! Which of the choices below indicates the source of your problem?（）

• A、Hardware failure in NVRAM prevents the router from loading the config
• B、Startup-config in flash is corrupt and cannot be analyzed
• C、Router configuration-register set to bypass startup configuration
• D、Startup-config in NVRAM is corrupt and cannot be analyzed
• E、None of the above