In earlier books, when using KARA, we were taught that the verb in the first clause sounds better in casual form. However I have noticed recently several examples where the formal form is used. This seems to be in cases where there isn't a second clause.
So, with a second clause, the casual is used: りょうりが下手だから、ケーキをかいました。 (because i'm bad at cooking, I bought a cake)
But without the second clause, would you say: りょうりが下手ですから。 OR りょうりが下手だから。 (because I'm bad at cooking) or would it depend on the formality of the conversation?
And, would you ever say: りょうりが下手だからです。 (It's because I'm bad at cooking)