Which command is used to change the platoon from a line formation?

The command used to change the platoon from a line formation is "RIGHT, FACE." This command instructs the members of the platoon to pivot 90 degrees to the right while maintaining their alignment in the formation. It effectively transitions the squad from a linear arrangement into a more manageable orientation for subsequent movements or formations, either for tactical purposes or while moving to another formation.

While the other options involve commands that have their own specific applications, they do not specifically indicate a transition from a line formation. "FORWARD, MARCH" would simply move the platoon forward without changing its formation, "ABOUT FACE" would turn them 180 degrees to face the opposite direction, and "LEFT, TURN" would generally involve a pivot to the left without altering the platoon's overall alignment in the same manner as "RIGHT, FACE." Thus, "RIGHT, FACE" is the most appropriate command for switching formation from a line.