More and more people choose to shop in a supermarket as it offers a great _____ of goods. A. combination B. mixture C. extension D. variety 答案:D14.跳伞运动员以5m/s的速度竖直匀速降落,在离地面h=10m的地方掉了一颗扣子,跳伞运动员比扣子晚着陆的时间为(扣子所受的空气阻力可忽略,g取10m/s2)( )A.2 sB.$\sqrt{2}$ sC.1 sD.(2-$\sqrt{2}$) s