When do interpretations or ethics rulings usually become effective?

The correct choice reflects a key aspect of the understanding of effective dates for interpretations or ethics rulings in the context of Certified Public Accountants. Ethics rulings are typically established to provide guidance and clarity on professional conduct and responsibilities. By stating that they become effective on the last day of the month in which they are published, it allows for a full month of preparation and adjustment for practicing CPAs.

This period is crucial, as it enables CPAs to digest the new information, assess its implications for their practices, and implement any necessary changes to align with the updated ethical standards. Such a timeframe ensures that professionals have enough time to adjust to the changes and integrate them into their operations without causing disruption.

By contrast, other timelines like immediate effectiveness or shorter grace periods could lead to confusion or rushed adaptations, potentially compromising the integrity of the accounting profession. Thus, the chosen option is aligned with the ethical framework's objective of promoting professionalism and adequate preparation.