Your computer has Windows 2000 Professional installed. Your office has a power outrage while you were running the disk defragmenter utility on your computer. When you start the computer again， you receive the following message： "Bad or missing OS". What should you do？（）

• A、Start the computer in safe mode and reformat the hard disk.
• B、Start the computer in the debug mode and reformat the hard disk.
• C、Start the computer using the ERD and repair the Master Boot Record.
• D、Start the computer by using the Windows 2000 Professional CD-Rom. Then use recovery console to repair the Master Boot Record.