In the quiz, I got the sentence
Antes de que tú digas nada, .... ( before you say anything )
Why is 'nada' here ? Can it be 'algo' ?
Another example from the other lesson is, though I don't remember the exact phase but it's like
No creo que hayan llegado todavía.
The original phase to be denied should be 'han llegado ya'. Again, why it changed to 'todavía' ?
I agree that whole expression has something negative, which hasn't happened yet. But I'm confused, because the phase in 'que' is totally affirmative.
So the expression in 'que' isn't independent from its use ? And how ?