Which guideline is correct for professional letter formatting?

• A. Half-inch margins, single-spaced body, single spacing between paragraphs, and sentences no longer than 30 words.
• B. One inch margins, double-spaced body, single spacing between paragraphs, and sentences no longer than 20 words.
• C. One inch margins, single-spaced body, double spacing between paragraphs, and sentences no longer than 15 words.
• D. One inch margins around the page; single-space body; double spacing between paragraphs; no more than 20-word sentences; 2-3 sentences per paragraph minimum; keep paragraphs under 10 lines.

Answer: (D)

Professional letter formatting aims for a clean, readable document suitable for business communication. Use one-inch margins on all sides to create a balanced frame and leave room for notes. The body should be single-spaced to keep the text compact while remaining easy to read; insert a blank line between paragraphs so there is clear separation—this is effectively double spacing between paragraphs. Sentences should be concise, no longer than about twenty words, which helps maintain clarity and reduces reader fatigue. Aim for two to three sentences per paragraph to keep ideas organized and to prevent long blocks of text. Keeping paragraphs under roughly ten lines helps readability on both screen and paper.

This combination matches typical professional letter standards, making it the best choice. Choices that use smaller margins or invert spacing patterns, or that push sentence length well beyond twenty words or create cramped or overly sparse paragraphs, would hinder readability and professional appearance.