Use of "did"

Hi,maybe because there has been the Verb paint,so we can't write did because did is a verb,too.If there's a Subject (I,You,We,They,He,She,It..'' we can use did to ask,for EX:''Where did you go?''...the Subject will stand between two Verbs are did and go.It's just my opinion,you should take some advices from other friends

Anonymous"Who painted that picture?".
My question is: Why it doesn't write "Who did paint that picture?" ?

Who, a question word, is the grammatical subject of the sentence and that's why did isn't used. In the same way: What happened? (Not: What did happen?)

CB

When a question word such as "Who" is the subject of the sentence, you may not use "do."

Who (subject) + painted (verb) + that picture (object).

One big EXCEPTION: You may use "do" if you demand an answer:

All of you say that you did not paint that picture. Well, I want to know

who DID paint that picture. = I INSIST on knowing who is responsible

for p

Anonymous"Who painted that picture?".
My question is: Why it doesn't write "Who did paint that picture?"

We don't use a form of do when we are not inverting subject and verb.

With inversion:

You painted that picture.
(You did paint that picture.) [Change to add did in preparation for inversion.]