可以使用Smart Grid-layout Extension 对于CF7C插件。智能电网插件具有[dynamic_dropdown] 标签，用于过滤选项。

add_filter(\'cf7sg_dynamic_dropdown_custom_options\', \'filter_options\',10,3);
function filter_options($options, $field_name, $form_key){
  if($form_key != \'my-form\') return $options; //check this is the correct form.
  if($field_name != \'bookings\') return $options; //check this is the correct field.
  $options = array();
  //load all your booking options.
  foreach($bookings as $booking){
    //verify if the booking limit is crossed.
    if($booking->count < $limit){
      $options[$booking->id] = $booking->title; //$options are $value=>$name pairs.
    }
  }
  return $options;
}