The Difference Between the Save and the Save as Commands

The difference between the Save and the Save As commands is that ____.

A) one is used with an existing file and one is used when a new file without a name is open
B) one is used with an existing file,and one is used when you need a new name
C) one is used with an existing file,and one is used when you want to save in a new location
D) all of the above