Ans: An extend relationship documents the extension of the functionality of the use case to incorporate optional behavior. For example, if the use case Register for Classes describes the registration process at your university, the use case Clear Financial Hold would only be executed for students who have financial holds on their registration, and the relationship between these two use cases would be an extend relationship. An include relationship represents the mandatory inclusion of another use case, which would happen if you had decomposed a particularly complex use case into several simpler ones. The text points out that this type of relationship allows for functional decomposition.Response: See page 170