Can I say "he’s done is so great" instead of "he’s done that’s so great"?
Native speaker’s answer
Rebecca
No, you can't replace "that's so great" with "is so great" here. Since this sentence asks the question "what", it must be followed by "that is", and not just "is". If the question word was "why" instead, then you could use "is" if you rearranged the sentence. Ex: What did you do that was so embarrassing? Ex: What do you think the age is that people can drink alcohol here?