To share a Cloud Monitoring custom dashboard with a partner team, the most effective method is to provide them with the dashboard URL. This allows the partner team to create a copy of the dashboard directly in their own Google Cloud environment, ensuring they have access to the most current data without the need for manual updates or additional steps. Option A is correct because it leverages Google Cloud's built-in sharing capabilities, making the process seamless and efficient. Options B, C, and D involve more manual processes or do not directly result in the partner team having a functional copy of the dashboard in their Cloud Monitoring environment.