CoA, or Change of Authorization, is a feature in Cisco ISE that allows the ISE server to dynamically change the attributes of an AAA session after it is authenticated. In this case, the CoA is sent to the NAD, or Network Access Device, after the user logs in successfully using CWA, or Cisco Web Authentication. The CoA will trigger the NAD to reauthenticate the client, which will allow the ISE server to verify the client's compliance status and apply the appropriate authorization policies.
Options A, B, and C are incorrect. The CoA does not terminate the client session, apply a downloadable ACL, or apply new permissions to the client session.