Option A is correct because using the gcloud command-line tool to create a new GCP project and then deploying the app to it ensures a clear separation between development and production environments, adhering to best practices. This separation minimizes potential impacts from development activities on the production environment. Options B and C are incorrect as they suggest modifications within the same GCP project, failing to provide the necessary environment separation. Option D is incorrect because specifying a new project name with the project parameter in gcloud does not create a new project but rather attempts to deploy to an existing one, which contradicts the requirement for a new production environment. For more details, refer to the GCP documentation on creating projects and deploying apps.