Which motion is considered out of order if a main motion is pending and a motion to amend is under debate?

When a main motion is pending and a motion to amend that main motion is under debate, the parliamentary rules dictate which motions can or cannot be entertained. In this specific situation, a motion to postpone indefinitely is out of order because it directly relates to the main motion and cannot be considered while amendments to that main motion are being debated.

This is due to the principle of maintaining order in the debate process; interruptions or additional motions that could confuse or derail the ongoing discussions on amendments are restricted. Postponing the main motion indefinitely would interfere with the current amendment process.

In contrast, a point of order or a parliamentary inquiry are motions that help facilitate the discussion or clarify the rules, and they do not interrupt the flow of debate in the same way. The motion to adjourn is also permissible, as it simply seeks to end the meeting without impacting the decision-making on the current main motion or its amendments. Therefore, postponing the main motion indefinitely when it is under amendment debate is not allowed, making this the correct choice.