code: func listSubnetworksOfNetwork(svc *compute.Service, networkProjectID, networkID, region string) ([]*compute.Subnetwork, error) {
  	var subnets []*compute.Subnetwork
  	err := svc.Subnetworks.List(networkProjectID, region).Filter(fmt.Sprintf("network eq .*/%v$", networkID)).Pages(context.Background(), func(res *compute.SubnetworkList) error {
  		subnets = append(subnets, res.Items...)
  		return nil
  	})
  	return subnets, err
  }
docs: // listSubnetworksOfNetwork returns a list of subnetworks for a particular region of a network.