① ____ A. summer B. winter C. season
② ____ A. which B. there C. why
③ ____ A. because B. pretty C. beautiful
在地面上,将一个小球以v=20m/s初速度竖直上抛,则小球到达距抛出点10m的位置所经历的时间为(g=10m/s2)( )