A Cisco router has been configured, and the copy running-config startup-config command has been issued. When the router is power cycled, the router prompts with: "Would you like to enter the initial configuration dialog? [yes/no]" Why has this occurred?（）

• A、There is an error in the router DRAM.
• B、Te IOS image is corrupt.
• C、The configuration register is set to 0x2142.
• D、The TFTP server that contains the router configuration file is unreachable.
• E、A boot system configuration command has placed the router into setup mode.