Complex sentence: The origin of the Balto-Slavic nouns of the mobile paradigm has not been completely determined, but the most probable and prevalent possibility is that proposed by Illič-Svityč, according to whom they originate as an analogical development from fixed-accent PIE oxytones.
Split into simpler sentences: The origin of the Balto-Slavic nouns of the mobile paradigm has not been completely determined, with several proposed theories of origin. According to Illič-Svityč, they originate as an analogical development from fixed-accent PIE oxytones.