The correct option is Perform a security control assessment.

A security control assessment is the formal activity used to verify that a control is implemented correctly and is operating effectively after a revision or new threat intelligence. The assessment applies test procedures and evidence collection to determine whether the control meets its security objectives and to identify any remaining weaknesses.

An assessment can include configuration checks, code review, functional tests, and targeted security testing to prove the control works in the environment and to provide documented evidence of effectiveness.

Cloud Security Command Center is a cloud provider tool that helps discover and surface security findings for Google Cloud resources. It is not the formal verification step that confirms an enterprise application control continues to operate effectively across the system.

Monitor the control as part of the ongoing continuous monitoring program is important for long term visibility and detecting trends. Continuous monitoring alone may not provide the focused, evidence based testing needed immediately after a control change to prove the control is functioning as intended.

Update the system security plan documentation is a necessary administrative action to keep records accurate. Updating documentation does not itself test or validate control operation so it cannot replace a security control assessment when confirmation of effectiveness is required.

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