是 Who stayed up late yesterday
因为who 是疑问词也是主语嗯，我同意你的答案。但老师却说是Who did，能不能告诉我，为什么Who也是主语问主语用WHO， 后不用加助动词

正确的一定是：Who stayed up late yesterday ?


区别： I went to Beijing with my parents last year.
Who did you go to Beijing with last year ?( 划线是my parents )
这里问的是宾语

Who went to Beijing with my parents last year? ( 划线是I ， 问的是主语）