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阅读材料，回答问题。 2017年8月，台州北部湾经济开发区设立，涵盖了三门全域。去年的9月份，三门接轨上海合作发展推介会在上海举行。一年多来，三门借着“大湾区”的发展东风，揭开了腾飞的序幕。某班以此为主题开展了一次社会调查活动，调查分为两个小组：第一组：通过查阅图册和搜索网络等途径，找有关“台州北部湾区”的资料。第二组：采访了县委书记杨胜杰，他说：三门与上海在经济上有共通，人脉上有共联，交流上有共识，情感 In fall 2006，the National Basketball Association （NBA）started using basketballs made with synthetic ，or man-made ，material instead of leather（皮革）．They made the change be- cause they wanted every basketball they use to feel and bounce（弹起）the same．Not all leather balls are exactly alike in weight or how they bounce，but the synthetic balls are． However，some players complained right away that the new balls bounced differently and were actually harder to control than the leather ones． Physics helped answer questions about why the new balls felt different．For example，the scientists studied friction（摩擦力），which in this case affects the ability of a player to hold onto a ball．"The greater the friction，the better it will stick to his hand，"explains a scientist． Tests on both wet and dry balls showed that while the synthetic ball was easier to hold onto when dry，it had less friction and became much harder to hold onto when wet．That's because sweat（汗水） stays on the surface of the synthetic balls but gets taken into the leather balls． The scientists also tested bounce and found that the logo （商标）printed on the new balls made their surface uneven（不平） and caused them to bounce a little strangely com- pared with the leather balls． In January，the NBA went back to using the leather bails．They aren't perfect，but for now，that's just the way the ball bounces． 1．Why were the synthetic balls expected to be used in NBA according to the text?        A．Because they are easier to control．           B．Because they waste less material．        C．Because they look exactly alike．             D．Because they feel and bounce alike． 2．The ball is easier to hold on to_________ A．when friction is greater                    B．when friction is less C．when it is heavier                         D．when it bounces strangely 3．The synthetic ball bounces differently from the leather one mainly because _________ A．it is wet                                  B．it is dry C．there's a logo on it                       D．its weight remains the same 4．It can be inferred（推断） from the text that _________． A．a synthetic ball takes in water faster than a leather ball B．a leather ball is more difficult to make than a synthetic one C．a synthetic ball is more expensive than a leather ball D．a leather ball may increase its weight during a game 5．The underlined word" They" in the last paragraph refers to __________． A．the synthetic balls                        B．the leather balls C．the ball players                          D．the scientists