I thought 'czyste'. Why is it 'czysto'?
"Czysto" is an adverb. "Czyste" is an adjective and it would have to describe some neuter or non-masculine-personal noun, the word "to" or pronoun "ono".
Is "nigdy nie" never, while "nigdy" means ever?
I don't believe that there is such a sentences containing "nigdy", but without "nie". Unless it's a one word sentence. But even then it means "never".
So does the construction sometimes mean "not ever"? Nigdy is defined as never or ever (when I use the translation function by clicking on the underlined word).
Do you see a semantical difference between:
Why is the adverb allowed to be at the end of the sentence here?