code: def GetMACBRepresentationFromDescriptions(self, timestamp_descriptions):
      
      macb_representation = []
  
      if ('mtime' in timestamp_descriptions or
          definitions.TIME_DESCRIPTION_MODIFICATION in timestamp_descriptions):
        macb_representation.append('M')
      else:
        macb_representation.append('.')
  
      if ('atime' in timestamp_descriptions or
          definitions.TIME_DESCRIPTION_LAST_ACCESS in timestamp_descriptions):
        macb_representation.append('A')
      else:
        macb_representation.append('.')
  
      if ('ctime' in timestamp_descriptions or
          definitions.TIME_DESCRIPTION_CHANGE in timestamp_descriptions):
        macb_representation.append('C')
      else:
        macb_representation.append('.')
  
      if ('crtime' in timestamp_descriptions or
          definitions.TIME_DESCRIPTION_CREATION in timestamp_descriptions):
        macb_representation.append('B')
      else:
        macb_representation.append('.')
  
      return ''.join(macb_representation)
docs: Determines the MACB representation from the timestamp descriptions.
  
      MACB representation is a shorthand for representing one or more of
      modification, access, change, birth timestamp descriptions as the letters
      "MACB" or a "." if the corresponding timestamp is not set.
  
      Note that this is an output format shorthand and does not guarantee that
      the timestamps represent the same occurrence.
  
      Args:
        timestamp_descriptions (list[str]): timestamp descriptions, which are
            defined in definitions.TIME_DESCRIPTIONS.
  
      Returns:
        str: MACB representation.