Which of the following BEST indicates the effective implementation of a risk treatment plan?

Inherent risk is the risk level before any controls are applied; it cannot be 'managed' within an acceptable level because controls haven't been factored in yet.

A risk treatment plan aims to apply controls and mitigate identified risks. The ultimate measure of its effectiveness is whether, after applying these treatments, the remaining (residual) risk aligns with the organization's established risk appetite (the amount of risk it is willing to take) and tolerance (the acceptable deviation from that appetite).

While aligning with industry peers can be a useful benchmark, it does not directly confirm that the specific organization's unique risks are being effectively managed according to its own risk appetite and tolerance.

Identifying and documenting key controls is a step in developing a risk treatment plan, but it does not, by itself, indicate the effectiveness of its implementation in reducing risk to an acceptable level.