[SLUG] ask emacs(ediff)

[henry]

Dear List:   I use ediff to compare files by "M-x ediff". It's OK when these 2 files are under the same directory. But it' unconvenient to pick up 2 files under different directories.   I list buffer by "Ctrl-x Ctrl-b" But I cant pick up 2 files from buffer for input-files of ediff . Is there a convenient way to do it ?  Cause it's supposed that's why buffer exists for .     a newbie of Emacs