Misc: Eras are divided into units called ________?

Questions

90's Chart Toppers: Name The Artist: You Used To Love Me?

90's Chart Toppers: Name The Artist: You'll See?

90's Chart Toppers: Name The Artist: 1,2,3,4 (Sumpin'New)?

90's Chart Toppers: Name The Artist: 1979?

90's Chart Toppers: Name The Artist: All The Things (Your Man Won't Do)?