The document discusses the C's of effective communication in business letters:
1) Correctness - Letters must be correct in spelling, grammar, language, appearance and conveying accurate information.
2) Clarity - The message must be clear and easily understood using simple words, short sentences, proper punctuation and logical order.
3) Conciseness - Expressing ideas using as few words as possible while maintaining clarity and completeness.
4) Courtesy - Using polite words and phrases that are considerate of the recipient's feelings.
5) Completeness - Providing all necessary facts and figures to avoid misunderstandings.