If a Six Sigma Project Was to Reduce Changeover Times

If a Six Sigma project was to reduce changeover times and the team found the project success was decreasing over time since changeover times began to creep back up, which Lean tools should be considered in the Control Phase to reestablish and sustain the project success?  

A) Improve the lighting to assure adequate visibility
B) Confirm a Visual Factory exists to assure proper communication of status of machines
C) Implement Kanbans to assure enough inventory for the process step
D) Reword the standardized work instructions to use active verbs and not passive phrases