i need a help =" please ="

hi every one <3 , i wanna ask Du about a song and i hope Du can help me to know it ="
link
it is started from 3:01 to 3:11 ="

when Jeon Ah-min(Jo In-seong)with Ham Eunjung(Yoon Baek Hee) and the Teacher , the Teacher sagte : start ,
then Jo In-seong say the song ( the english lyrics in this part is :
( Hey , just like i believe in Du believe in my friend , therefore i to not be burdened to introduce Du to my Friends )
then the Teacher sagte : let it out , let it out

Du know it ? ="