Calling 2 or more subtypes in river

Hello!

Is there a way to call more subtypes than 1?

I'm using something like this but want to call something else along with groupforumtopic

$river = elgg_view_river_items ($subject_guid=0, $object_guid=0, $subject_relationship= '', $type= 'object', $subtype= 'groupforumtopic', $action_type= '', $limit=20, $posted_min=0, $posted_max=0, $pagination=true);