(The students)are singing in the classroom.就括号部分提出问题___________ _______ singing in the classroom

(The students)are singing in the classroom.就括号部分提出问题___________ _______ singing in the classroom
(The students)are singing in the classroom.就括号部分提出问题
___________ _______ singing in the classroom

(The students)are singing in the classroom.就括号部分提出问题___________ _______ singing in the classroom
Who is
画线部分是主语
所以用who
因为提问的时候不知道人称是单数还是复数
所以统一用单数is