Which component of a letter includes the sender's and recipient's addresses?

The heading is the correct choice because it typically includes both the sender’s address and the recipient’s address in a formal letter format. In this section, the sender’s address usually appears at the top, followed by the date and the recipient’s address. This layout helps to identify who the letter is from and who it is intended for, which is fundamental in correspondence.

The signature line is where the sender signs their name, usually placed at the end of the letter. The body contains the main content of the message being conveyed, while the conclusion consists of closing remarks or a sign-off. None of these components cover the addresses needed to identify the sender and recipient, making the heading the essential part that serves this purpose.