ans is B
You can edit more than one file at a time with vi.
From The Unix Shell Prompt
vi file1 file2 vi two (or more) files at the same time
From Command Mode
:n Move to file2 from file1
:rew Rewind back to file1
:e! Restore original file1 file2 (start all over)
ZZ Save and quit file. (Must be done for each file.)