"What is that smell?"
Translation:Bau apa itu?
I put 'bau itu apa' and was marked wrong. I think it's maybe a difference between 'I can't work out what that smell is', ('bau apa itu' or 'which is that smell') and 'what is that smell' as an exclamation, perhaps when you smell something unpleasant. But they really should accept both because the English doesn't make it clear.