题目

On December, 3, 2009, Philadelphia 76ers, ______ NBA team, held ______ news conference announcing Allan Iverson would return．        A．a; the       B．an; /  C．an; a  D．the; / 答案：C如图中，光滑接触面对球和棒的弹力分析正确的是（　　）A．B．C．D．