一根长60cm的细绳，最多能承受100N的拉力，用它吊起一质量为4kg的物体，当物体摆动起来经过最低点时，绳子恰好被拉断．若绳断处距离地面的高度为0.8m，求物体落地时的速度大小．（不计空气阻力，g=10m/s²）

读一读，把正确答案代码填入相应的括号里。

① What can you do?____      A. I need a new dress.

② What can she do?____      B. I can ride a bicycle.

③ What can he do?____       C. She can fly a kite.

④ What do you need?____   D. He can play football.