The BEST information when determining whether to accept residual risk of a critical system to be implemented is the potential business impacts are within acceptable levels, because it indicates that the residual risk, which is the risk that remains after the risk response actions, does not exceed the risk tolerance and appetite of the organization, and that it does not pose a significant threat or disruption to the business objectives and processes. The potential business impacts are the consequences or outcomes of the residual risk on the organization’s performance, reputation, and value. The other options are not as informative as the potential business impacts, because:

Option A: Single loss expectancy (SLE) is a measure of the monetary loss that is expected from a single occurrence of a risk event, but it does not provide the best information when determining whether to accept residual risk, because it does not consider the frequency or probability of the risk event, or the qualitative aspects of the risk impact, such as customer satisfaction, employee morale, or regulatory compliance.

Option B: Cost of the information system is a measure of the total expenditure that is required to acquire, develop, operate, and maintain the information system, but it does not provide the best information when determining whether to accept residual risk, because it does not reflect the value or benefit of the information system, or the risk exposure or variation that the information system may introduce or encounter.

Option C: Availability of additional compensating controls is a measure of the alternative or supplementary controls that can be implemented to reduce the residual risk, but it does not provide the best information when determining whether to accept residual risk, because it does not indicate the effectiveness or efficiency of the compensating controls, or the cost-benefitanalysis of implementing them. References = Risk and Information Systems Control Study Manual, 7th Edition, ISACA, 2020, p. 122.