what should be written in a formal style?\npersonal e-mails\nfriendly letters\nmovie reviews\nwork documents

Brief Explanations:

Personal e - mails and friendly letters are usually written in an informal style as they are between people who know each other well. Movie reviews can have a more creative and less formal tone. Work documents, on the other hand, are often used in a professional context where a formal style is required for clarity, respect, and to maintain a professional image.

Answer:

work documents