Extreme Programming (XP) is a discipline of software development with (71) of simplicity, communication, feedback and courage. Successful software development is a team effort - not just the development team，but the larger team consisting of customer, management and developers. XP is a simple process that brings these people together and helps them to succeed together. XP is aimed primarily at object-oriented projects using teams of a dozen or fewer programmers in one location. The principles of XP apply to any (72) project that needs to deliver quality software rapidly and flexibly. An XP project needs a(an) (73) customer to provide guidance. Customers， programmers, managers, are all working ( 74 ) to build the system that’s needeD. Customers — those who have software that needs to be developed - will learn simple, effective ways to (75) what they need, to be sure that they are getting what they need, and to steer the project to success.