The correct answer is A. One or more of the constraints might move . In the CSSBB control-phase material, the project control phase is described as necessary to sustain the project gains , and the control plan must remain a living document so the process can continue to be monitored and updated over time. The supplemental Lean Six Sigma material also states that the Control phase ensures that the new performance of the Y is sustained over time and that a monitoring system should continually track leading X’s and lagging Y indicators.

This ongoing monitoring is especially important because, in Theory of Constraints, once one constraint is improved or broken, the system must return to step 1 and look for new constraints . The CSSBB source explicitly states, “After the constraint has been broken, look for new constraints.” That means the location of the bottleneck or limiting factor can shift after improvements are made. Option B is too narrow, option C is not a valid control-phase principle, and option D incorrectly assumes another pilot run is the reason for monitoring. Therefore, the best verified answer is A .