Apink's songs pair catchy melodies with strings and peppy dance beats. In that sense, they're a throwback to '90s girl groups like S.E.S. and Fin.K.L. The seven-member outfit debuted in 2011 with "I Don't Know," which was the first in a string of hits boasting massive choruses and sunshiny lyrics. Much like those of their forebears, Apink's songs draw strong inspiration from R&B. You can hear it in singles like "NoNoNo," and especially on slower tracks like the acoustic guitar-driven "Sunday Monday," which also doubles as a showcase for their sweet vocals.