<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_parent_classes_transparent(cls, slot, page, instance=None):
 """ Return all parent classes including those marked as "transparent". """

        parent_classes = super(CascadePluginBase, cls).get_parent_classes(slot, page, instance)
        if parent_classes is None:
            if cls.get_require_parent(slot, page) is False:
                return
            parent_classes = []

        # add all plugins marked as 'transparent', since they all are potential parents
        parent_classes = set(parent_classes)
        parent_classes.update(TransparentContainer.get_plugins())
        return list(parent_classes)