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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_instance():
 """Get a resource based on the application environment. Returns a `Resource` configured for the current environment, or None if the environment is unknown or unsupported. :rtype: :class:`opencensus.common.resource.Resource` or None :return: A `Resource` configured for the current environment. """

    resources = []
    env_resource = resource.get_from_env()
    if env_resource is not None:
        resources.append(env_resource)

    if k8s_utils.is_k8s_environment():
        resources.append(resource.Resource(
            _K8S_CONTAINER, k8s_utils.get_k8s_metadata()))

    if is_gce_environment():
        resources.append(resource.Resource(
            _GCE_INSTANCE,
            gcp_metadata_config.GcpMetadataConfig().get_gce_metadata()))
    elif is_aws_environment():
        resources.append(resource.Resource(
            _AWS_EC2_INSTANCE,
            (aws_identity_doc_utils.AwsIdentityDocumentUtils()
             .get_aws_metadata())))

    if not resources:
        return None
    return resource.merge_resources(resources)