I don't exactly know WHY, but I can guess..
I think it's because, if you're writing, you can know where the source is from if you print the WHOLE SCREEN, or just to remember what the electronic source says.
I believe it is B hope this helped you<span />
It is A outputting (if you want I can show what it says in the dictionary)
C. Send it to the recycle bin and empty the recycle bin