What steps are required to make sure that the effects of this action are reverted as soon as the condition that triggered it is NO longer fulfilled?

You are implementing a new custom promotion action that changes the delivery mode of an order.

What steps are required to make sure that the effects of this action are reverted as soon as the condition that triggered it is NO longer fulfilled? Note: There are 2 correct answers to this question.
A . Implement the undo method in your custom rule action strategy
B . Define a new session attribute to store the original delivery mode
C . Implement your custom action item so that it can store the original delivery mode
D . Create a promotion that uses the inverse action if the condition is NOT fulfilled

Answer: A, C