The libero replacement may occur only one time per dead ball. That means that after the libero has rotated from LB (or CB) to the RB position to serve and subsequently rotates across the back row, when the libero would rotate from LB into LF, the player whom she (or he) replaced must return to the court. The libero must remain out for one rally. At the conclusion of one rally or replay (NOT reserve, however), the libero may replace any of the three players in the back row. So, with the three options that you have given, the most correct answer is A.
Remember that the libero serving is experimental for this school year, so you should verify that what I said above is accurate in your particular state - give a call to Gina at MHSAA and she will give you the proper interpretation. Next year, the libero serving will be part of the rules and we will have the specifics within the body of the rules book.