The correct answer is option 'B' - 5.

A letter is a written form of communication that is used to convey messages or information between individuals or organizations. It typically consists of several parts, each serving a specific purpose. Let's break down the different parts of a letter:

1. Heading:
- The heading is the top part of the letter and includes the sender's address and the date. It is usually positioned on the right-hand side of the paper.

2. Inside Address:
- The inside address includes the recipient's name, job title, organization, and address. It is placed below the heading on the left-hand side of the paper.

3. Salutation:
- The salutation is the greeting at the beginning of the letter, addressing the recipient. Common salutations include "Dear" followed by the recipient's name or title, such as "Dear Mr. Smith" or "Dear Hiring Manager."

4. Body:
- The body of the letter contains the main content or message. It is where the sender expresses their thoughts, requests, or provides information. The body is typically divided into paragraphs, each focusing on a specific point.

5. Closing:
- The closing marks the end of the letter and is followed by the sender's name. Common closings include "Sincerely," "Yours truly," or "Best regards." The sender's name is usually positioned below the closing and may be accompanied by their job title or organization.

In summary, a letter consists of five parts: the heading, inside address, salutation, body, and closing. These parts help structure the letter and ensure effective communication. By following this format, the sender can convey their message clearly and professionally.