What were they doing differently that had led to this dramatic improvement?
I saw a sentence having the same structure as the one above. But I am not sure that this sentence is grammatically correct. I would like to know your opinions.
The "that" in the sentence seems a relative pronoun, but where is the antecedent? When I speculate what it says, the antecedent could be the "what". Is it possible?
what. Clearly it's not a noun but an action. The Wh-clause itself is an NP, though, so it can take a relative clause. – John Lawler Sep 26 '15 at 15:25