i think sooyoung and tiffany sang this part
[tiffany+sooyoung]*geudaereul boreumyon geudaereul chajeumyon
baramee dwi oso naegyote wajwoyo
[taeyeon and yoona] *geudaereul boreumyon geudaereul chajeumyon
Haessali dwioso nae gyote wajwoyo
[taeyeon] Iroghe soomanheun choo ogeul namgigo
[all] Ojik nan geurae man saengak haneun de (taeyeon sing this part not all )
(Hyoyeon sing this part and jessica * i think) Geudaereul booreumyon geudaereul chojeulmyun
Bitmoolee dwe oso naegyote wajwoyo
thats my opinion cause i can spot hyoyeon voices here
btw love this song....
This's what i've been thinking too