Complex sentence: First, UCLES explored the viability of an exam below LCE (renamed as First Certificate in English) and the Preliminary English Test (PET) (re) appeared in 1980 under close monitoring, and as a fully-fledged exam in the 1990s.
Split into simpler sentences: First, UCLES explored the viability of an exam below LCE (renamed as). The (re) appeared in 1980 under close monitoring, and as a fully-fledged exam in the 1990s.