What is the difference between the i and a commands of the vi editor?

[answerhappygod]

What is the difference between the i and a commands of the vi editor?

A. i (interactive) requires the user to explicitly switch between vi modes whereas a (automatic) switches modes automatically.
B. i (insert) inserts text before the current cursor position whereas a (append) inserts text after the cursor.
C. i (independent rows) starts every new line at the first character whereas a (aligned rows) keeps the indentation of the previous line.
D. i (interrupt) temporarily suspends editing of a file to the background whereas a (abort) terminates editing.