The more subtle ones I was unable to pick up on. To me, when people spoke, it sounded monotone, especially on those audio exercise sounds played over speakers. I don't have a problem picking up on the tonal differences in English, because the difference is quite a bit more pronounced to me.

EDIT: I should also point out that asking a question does not require the shift in tone for it to be understood as a question, e.g., saying 'What are we doing next?' without any change in tone is perfectly fine.