Answer:

Enclosing a self-addressed and stamped envelope with a questionnaire is referred to as a covering letter. A covering letter is a document that is sent along with another document, such as a questionnaire, to provide additional information or instructions. In this case, the covering letter includes a self-addressed and stamped envelope for the recipient to easily return the completed questionnaire.

Explanation:

A covering letter serves as a way to introduce the main document and provide context or instructions. In the case of a questionnaire, the covering letter typically explains the purpose of the questionnaire and includes any specific guidelines or instructions for completing it. By enclosing a self-addressed and stamped envelope, the sender ensures that the recipient can easily return the completed questionnaire without incurring any costs for postage.

The self-addressed envelope includes the sender's address, making it convenient for the recipient to simply place the completed questionnaire inside and mail it back. The envelope is also pre-stamped, meaning that the sender has already paid for the postage, further facilitating the return process.

This practice is commonly used in research studies, surveys, or other situations where collecting data or feedback is necessary. By including a self-addressed and stamped envelope, the sender increases the likelihood of receiving a response, as it eliminates any barriers or inconvenience for the recipient.

In summary, a self-addressed and stamped envelope enclosed with a questionnaire is called a covering letter. This method streamlines the process of returning the completed questionnaire and increases the chances of obtaining the desired information or feedback.