Question about actions on record modifications

So I'm trying to create an action that when a record is modified it creates a task. That is simple enough. Though, there are two fields that need to be modified to trigger this action. Lets call them [Field A] and [Field B]. So when both [Field A] and [Field B] are no longer blank the action fires. Though, [Field A] could be filled in on Monday and [Field B] on Tuesday, or they could both be filled in on the same day. This is because this information may be gathered at a time later then when the record is created. Will this require 3 actions?

1. When the record is modified, and the specific fields [Field A] and [Field B] change and [Field A] and [Field B] are no longer blank, the action fires.

2.When the record is modified, and [Field A] changes and [Field A] and [Field B] are no longer blank, the action fires.

3.When the record is modified, and [Field B] changes and [Field A] and [Field B] are no longer blank, the action fires.

Or does the specific fields change only require one of the fields specified to change to fire and I will only need the first action?