题目

阅读短文，根据其内容，选择最佳选项完成下列各题。In fall 2006,the National Basketball Association(NBA)started using basketballs made with synthetic(合成纤维) ,or man-made material instead of leather(皮革).They made the change because 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 q9．若不等式x2+2$\sqrt{2}$xy≤a（x2+y2）对于一切正数x，y恒成立，则实数a的最小值为2．