The standard operating procedure (SOP) statement that best illustrates appropriate risk register maintenance is to remove risk when mitigation results in residual risk within tolerance levels. Residual risk is the risk that remains after the risk response or mitigation has been applied. Tolerance levels are the acceptable or allowable ranges of variation or deviation from the expected or desired outcomes or objectives. When the mitigation results in residual risk within tolerance levels, it means that the risk has been reduced or managed to an acceptable or satisfactory level, and that no further action or monitoring is required. Therefore, the risk can be removed from the risk register, as it is no longer a significant or relevant risk for the organization. The other options are not as appropriate as removing risk when mitigation resultsin residual risk within tolerance levels, as they are related to the transfer, acceptance, or change of the risk, not the removal of the risk. References = Risk and Information Systems Control Study Manual, Chapter 2: IT Risk Assessment, Section 2.4: IT Risk Response, page 87.