种子萌发的必要条件是____ ,____ ,____ .
下列a、b、c、d四图都与细胞分裂有关,相关描述正确的是
We were dying to hear the announcement of the winner of the race.
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)