Complex sentence: From 1961 to 1970,120 cars were built by Hitachi Ltd. Starting in 1990,6000 series was began to be replaced by Sōtetsu 8000 series and Sōtetsu 9000 series EMUs.
Split into simpler sentences: From 1961 to 1970,120 cars were made by Hitachi.Ltd. Starting 1990,6000 series was began to be replaced by Sōtetsu 8000 series and Sōtetsu 9000 series EMUs.