Which of the following statements about cover letters is WRONG? ( )

A、When submitting a cover letter by email or online, using a .doc file rather than a .pdf file makes it looks cleaner and more professional.
B、A cover letter is a one-page document that is designed to introduce and explain submitted material, such as a job application or an article for a magazine.
C、Cover letters are provided for editors only, which means that, the cover letter is going to be seen and read by a very tiny group of people.
D、A cover letter written to submit articles to magazines generally contains some key information about the research, such as background, aims, results and conclusion.