Business letters produce immediate effect because they are:

This answer is wrong. it is rather formal because, a business letter uses a rule based system and it is structured. Because of it's tone and formality, and often making request, compliants, and giving instructions, it aids immediate response.

Business letters produce immediate effect because they are formal. Formality in business letters conveys professionalism and seriousness, which can lead to an immediate impact. Business letters are not necessarily interesting, brief, or informal. They follow a specific format and tone to communicate effectively in a professional setting

Business letters are not informal but are formal and one reason is that they are official and use formal words.

Business letters are not informal but are formal and one reason is that they are official and use formal words.

answer should be formal

please correct the answer. It should be Option C

Why are business letters informal according to the question?

I think there's something wrong with the question or the answer. Aren't business letters formal