Complex sentence: The telethon was held two months after the historic plebiscite remembered October 5 that year and was the last telethon, which took place under the military government of Augusto Pinochet.
Split into simpler sentences: The telethon was held two months after the well-remembered and historic plebiscite of 5th. October that year and was the last telethon which took place under the military government of Augusto Pinochet.