1. Which one is correct? Sorry but this is the question.

Which one is correct?

Which is correct?

I still got no answer.

I still got no answers.

2. Would you put that or who here? I think GG said, in all possible situations when the word it is referring to is a person, it is better to use who but putting so many whos may make the sentence to look awakward.

Who is the person that or who??? invented the telephone?
Hi Believer,

1 - Both of your "Which... is correct" are okay, to my ears.

If you are speaking in the present tense, I still HAVE no answer or answers, depending on the context.

I've been strugging with this math problem for an hour, but I still have no answer. (A single answer to the math problem.)

I've asked many people about the meaning of life, but I still have no answers. ("Answers" to a larger, metaphysical question.)

If you are in the past, then "got" is okay, but it read funny to me at first, assuming that you meant the present.

2. Because I'm a nut about this, I would rewrite it: "Who invented the telephone?" And I'd rather have "who is... who" than a that.

I agree that sometimes it's useful as a restrictve clause, to differentiate the person from others in a similar group: My husband that is six feet tall was able to put the glasses on the top shelf - leads you to wonder how many husbands I have, versus My husband, who is six feet tall, was able to put the glasses on the top shelf.

But I admit it - I'm a jerk about this. When I was single, I wouldn't answer the personal ad for someone who wrote "I'm looking for a woman that..." - I got to that, and I was done. If he couldn't say "a woman WHO" I wasn't going to read any more. (Unless he was really cute Emotion: wink) So I'm probably not your best gauge. Clive has his semi-colon aversion, and I have this.
If I were going to list the possibilities after the question, I'd say Which one is correct?
The two are pretty much interchangeable, however.

With a negative it usually doesn't matter much whether you use the singular or the plural. Context may affect your choice. It may depend on how many answers you were expecting in this particular case. Use either answer or answers. (I'd say I still don't have an answer.)

The two who's so close together would bother me. It makes a 'who-who' sentence! This would make me tend to choose that. (Sorry, GG!) Nevertheless, who is perfectly fine grammatically, as you know.

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Grammar Geek... I'm a nut about this

But I admit it - I'm a jerk about this.

No apologies. I fully recognize that my views are little... uh... more firmly held Emotion: smile

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He has no teeth. (One normally has more than one tooth.)

He has no nose. (One normally has only one nose.)

I have no answer.

I have no answers.

Which sentence is correct