Complex sentence: The fourth season, 1971-72, saw a radical change in the series: the entire cast other than Doris Day had left the show: even Doris Martin's two sons were no longer in the cast.
Split into simpler sentences: The fourth season, 1971-72, saw a radical change in the series. The entire cast other than Doris Day had left the show: even Doris Martin's two sons were no longer in the cast.