/**
  * @param ProjectModel $projectModel
  * @param string $questionId
  * @param QuestionModel $questionModel
  * @return string activity id
  */
 public static function addQuestion($projectModel, $questionId, $questionModel)
 {
     $activity = new ActivityModel($projectModel);
     $text = new TextModel($projectModel, $questionModel->textRef->asString());
     $activity->action = ActivityModel::ADD_QUESTION;
     $activity->textRef->id = $questionModel->textRef->asString();
     $activity->questionRef->id = $questionId;
     $activity->addContent(ActivityModel::TEXT, $text->title);
     $activity->addContent(ActivityModel::QUESTION, $questionModel->getTitleForDisplay());
     $activityId = $activity->write();
     UnreadActivityModel::markUnreadForProjectMembers($activityId, $projectModel);
     UnreadQuestionModel::markUnreadForProjectMembers($questionId, $projectModel);
     return $activityId;
 }