Complex sentence: In 1971, the SABC was finally allowed to introduce a television service, which began experimental broadcasts in the main cities in mid- 1975, before the service went nationwide at the beginning of 1976.
Split into simpler sentences: In 1971, the SABC was finally allowed to introduce a television service. Experimental broadcasts in the main cities were performed in mid- 1975, before nationwide service commenced at the beginning of 1976.