Whether "did" or without at the Interrogative form?
In my Grammar book there is a task to put the sentence into a correct form. And there is a sentence:
1. "Who______(invent) the telephone?".
My version of sentence is:
2. "Who did invent the telephone?"
But in the keys to this task the sentence looks as below:
3. "Who invented the telephone?'
Can anybody explain me, why in the interrogative form of the key sentence 3 it doesn't use the auxiliary verb "did"?

Question

Answer

This is simple if you know the rule: We only need to add “did” when we invert the subject and the verb (i.e. put the subject after the verb). “Who” comes at the beginning of the question, so we do *not* (and cannot) use inversion when “who” is the subject:

Who saw them?

We use inversion for all other subjects, whether or not “who(m)” is the object:

Who(m) did they see?

Answer

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Answer

You're right, English questions often use 'did'. Where did you go? What did she do? When did they arrive? How did they come?

But it is very rare to use 'did' with 'who', unless you are using 'did' in its base meaning 'to do', rather than as an auxiliary verb: Who did that? (This is a correct question)

There is a very limited set of contexts where your sentence 2 would be correct. For example 'I wonder who did invent the telephone' with spoken emphasis on the word 'did'. And even in these contexts, sentence 3 would be perfectly OK.

Sentence 3 is the normal form of the question. I hope this helps.

Answer

No, I cannot answer why the auxiliary word is not needed in this interrogative sentence, but I can say that the auxiliary is also not used in the declarative sentence. "Alex invented the telephone." Not "Alex did invent the telephone." I hope that helps. Most grammar points are pretty much unknown to native English speakers.