Complex sentence: A voiceless alveolar trill occurs in Welsh, where it is spelled ˂ rh ˃; and in Ancient Greek, where it was spelled and has since merged with in Modern Greek.
Split into simpler sentences: A voiceless alveolar trill occurs in Welsh, where it is spelled "rh". It is postulated to have occurred in Ancient Greek, where it was spelled ""; this sound has since merged with in Modern Greek.