I’m back! Memory recall

Hello! I finally feel well enough that I’m not wholly thinking about my mouth pain.

So, recalling what I’ve learned.

です（Desu） – it is
じゃありません（Jaarimasen） – it is not
でした　(Deshita) – it was
じゃありませんでした (Jaarimasen deshita) – it was not

You can add　か (ka) to the end of them to turn them into questions,

何ですか？