public function GetAssignmentsForHIT($hit_id)
 {
     $params = array('HITId' => urlencode($hit_id));
     // For full functionality, implement setOption for options
     $request = new MechanicalTurkRequest("GetAssignmentsForHIT", $params, $this->options['sandbox']);
     $res = $request->go();
     // TODO: implement paging for multiple answers.  This method should return an array of assignments.
     if ($res->OperationRequest->Errors) {
         $this->print_errors($res->OperationRequest->Errors->Error);
         return false;
     } else {
         if (intval($res->GetAssignmentsForHITResult->NumResults) == 1) {
             return MechanicalTurkAssignment::fromSimpleXML($res->GetAssignmentsForHITResult->Assignment);
         } else {
             return NULL;
         }
     }
 }