Final answer:
A business letter is usually written in a block format, which includes left-justified text, single-spaced paragraphs, and double spacing between paragraphs. Therefore, the most appropriate option is C.
Step-by-step explanation:
A business letter is typically written in a block format. This format follows a formal style and specific form that includes left-justifying all elements, using a single space within paragraphs, and a double space between paragraphs. Key components of a business letter include the sender's address, date, recipient's address, salutation, body, and closing. A common font such as size 12 Times New Roman or Arial is also recommended for readability.