Complex sentence: On December 7th of that year, he was in Independence, Texas, with Professor Bill Caudell and two other students looking at old regional buildings when they heard on the radio that Pearl Harbor had been attacked.
Split into simpler sentences: On December 7th of that year, he was in Independence, Texas, with Professor Bill Caudell and two other students looking at old regional buildings. They heard on the radio that Pearl Harbor had been attacked.