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 (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.
73（）
A．part-time
B．casual
C．seldom
D．full-time
kg的木块A套在水平杆上，并用轻绳将木块与质量
kg的小球B相连。今用跟水平方向成α=30°角的力
N，拉着球带动木块一起向右匀速运动，运动中M、m相对位置保持不变，取g=10m/s2。求：
为多大时，使球和木块一起向右匀速运动的拉力最小？
