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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _reorder_fields(self, ordering):
 """ Test that the 'captcha' field is really present. This could be broken by a bad FLUENT_COMMENTS_FIELD_ORDER configuration. """

        if 'captcha' not in ordering:
            raise ImproperlyConfigured(
                "When using 'FLUENT_COMMENTS_FIELD_ORDER', "
                "make sure the 'captcha' field included too to use '{}' form. ".format(
                    self.__class__.__name__
                )
            )
        super(CaptchaFormMixin, self)._reorder_fields(ordering)

        # Avoid making captcha required for previews.
        if self.is_preview:
            self.fields.pop('captcha')