code: def get_inner_keys(dictionary):
      
  
      keys = []
  
      for key in dictionary.keys():
          inner_keys = dictionary[key].keys()
          keys += [
              key + " " + inner_key  # concatenate
              for inner_key in inner_keys
          ]
  
      return keys
docs: Gets 2nd-level dictionary keys
  
      :param dictionary: dict
      :return: inner keys