The correct answer is 'Implementing compensating controls'. Compensating controls are alternative measures that are put in place when standard security practices cannot be applied. In the case of legacy systems, where patching may not be feasible due to the lack of vendor support, compensating controls can help in mitigating risk by providing additional layers of security without altering the legacy systems themselves. This may include network segmentation to limit exposure, or more stringent monitoring to detect any malicious activity. 'Accepting the risk' is generally not advised unless the risk is very low or no other options are viable. 'Decommissioning the systems' might be a potential solution but it's not always the best if the system is still required for business operations. 'Applying unsupported patches' is incorrect because it poses a high risk of incompatibility, instability, or further security vulnerabilities.