When is "did" needed in questions using simple past?

Question

1. Who did find my keys?
   is wrong "Who found my keys?" is right

while:

2. Which film did you see yesterday evening?
   is right.
3. Why did she phone you yesterday?
   is right.

Those are question I answered at face2face course.

Answer 1

It isn't just about the past simple tense form but about whether you want to ask about a subject or an object. We usually use the wh-words who, whose, which and what both as subject and object but with a slight difference. For example:

• Who is the best footballer in the world? (who as subject) (He is the best footballer because.....)

• Who did you meet? (who as object) (I met Dunken...)

• What happened after that? (what as subject) (This was what happened next...)

• What did you say? (what as object). (I said thatshe left ...)

• So The question here Who Did Find My Keys? is wrong because you ask about the subject( suppose the answer is: Sue found my keys). So "Who Found My Keys?" is correct.