Which of the following statements about business letters is WRONG? ( )
选项：

A:A business letter is a type of correspondence between companies or between companies and individuals, such as customers, clients, contractors or other outside parties.
B:The body of a business letter expresses the writer’s idea, opinion, purpose and wishes.
C:Business letters and personal letters have the same tones and writing styles.
D:Informal words like “tell”, “or”, and “so” are not proper expressions in a business letter.