Which of the following problems has occurred when a menu appears and prompts the user to "copy a dump to external media?（）

• A、 The external dump device is full. 
• B、 The dump device was set to /dev/hd7 before the dump happened. 
• C、 The boot failed while copying the dump from paging space to a file. 
• D、 The dump device was not set to a paging device before the dump happened.