GRAMMAR CORNER: QUASI and QUESTIONS WITHOUT AUXILIARY

Last night the adult class was about questions with and without auxiliary.
On the whiteboard I wrote the following questions:

1) What song did Robbie Williams sing* with Nicole Kidman in 2002?
2) Who sang I can't get you out of my head?

sing is an irregular verb sing-sang-sung

Both questions are in past simple but in the first one there is the auxiliary did while in the second one there is no auxiliary verb. Why?
Let's see together

To make questions in the present and in the past simple, we normally use the auxiliary (do/does/did)  + infinitive without to (base form).

QUASI

QUESTION WORD	AUXILIARY	SUBJECT	INFINITIVE WITHOUT TO
What music	do	you	like?
Which CD	did	he	buy?
Who	did	she	go with?

However, when the question word is the subject (who/what/which/) WE DO NOT USE ANY AUXILIARY.

SUBJECT	VERB
What	happened	after the concert?
Who	writes	their songs?

Would you like to practice now?
Do the exercise!