Which command is given to extend the interval while marching?

The command "EXTEND, MARCH" is correct for extending the interval while marching because it is a standard command used in military drill. When this command is given, it signals the formation to adjust the distance between individuals, thus providing more space while maintaining the flow of the march. This command is precise and clear, allowing for immediate recognition and action from the troops.

In the context of military commands, terminology is essential for clarity in execution. Other phrases, while they may convey a similar intention, do not align with the established vocabulary of military drill commands. Therefore, using "EXTEND, MARCH" maintains consistency with the proper protocols established in drill and ceremony training. It reinforces discipline and uniformity among service members, which is critical in military operations.