Confirmation dialog wording standards

On macOS it seems usual to ask the user a (bold written) question in a confirmation dialog and add a more detailed text (non-bold and slightly smaller font). Regarding the bold question - should it be a complete sentence, e.g. "Do you want to delete file 'foo.txt'?", or would it be fine to write an incomplete sentence, e.g. "Delete file 'foo.txt'?"?