请用英文回答：Should postscript be written often？
举一反三
- 请用英文回答：What documents are often enclosed in business letters?
- 请用英文回答：Why should business letters be marked Reference？
- 请用英文回答：What should the writer do if he want to achieve clarity ?
- 请用英文回答：In Middle Paragraph, what necessary background and supporting information should be beprovided?
- what information should a poster include?一份海报一般包括几方面的要素？（请用英文回答））