sentences:  "The Big 600" flourished as a Top 40 rock station during the 1960s and 1970s before changing to a country format in 1981.In its final years as a Top 40, WTAC helped introduce the Australian heavy metal band AC/DC to American audiences.During the early and mid-1990s WTAC operated as a contemporary Christian music station; the WTAC calls are now used on Smile FM's 89.7 FM signal in the Flint area.