Help Detective Barnaby interrogate the bewildered bakery witness by selecting the correct question forms for his report.
"Alright, let's get the facts straight. First, tell me: who _________________________ the giant chocolate cake from the display window? And more importantly, who _________________________ running away from the scene with frosting on their face?"
The correct answers are stole and did you see.
When "who" is the subject of the question (the person doing the action, like stealing the cake), we do not use the auxiliary verb "did". We just use the past tense verb: Who stole the cake?
When "who" is the object of the question (the person receiving the action, like the person being seen), we must use the auxiliary verb "did" + the subject + the base verb: Who did you see?