Complex sentence: In 1971 the inner circle of line 3 (3A) was closed down, which would have made it possible to utilize the RM 2s on the remaining 3B, but this was not done.
Split into simpler sentences: In 1971 the inner circle of line 3 (3A) was closed down. This would have made it possible to utilize the RM 2s on the remaining 3B, but this was not done.