by mistake

他不小心删除了重要文档。

He deleted the important document ___by ___mistake.

我误拿了你的伞，以为是我的。

I took your umbrella ___by ___mistake, thinking it was mine.

我不小心拿错了别人的书。

I picked up someone else's book ___by ___mistake.

我不小心付了两次账单。

I've paid this bill twice ___by ___mistake.