从地面竖直向上抛出一个物体，当它的速度减为初速度v0的一半时，上升的高度为（空气阻力不计）( ) A．v02/2g B．v02/4g
已知向量a=(x-1,2),b=(4,y),若a⊥b,则9x+3y的最小值为 .
细胞分化是生物界普遍存在的一种生命现象，下列不正确的是（ ） 分化发生在生物体的整个生命进程中 分化是基因在特定的时间和空间条件下选
There once was a little boy who wanted to meet the king. He set off, walking towards the king’s castle. After many years of walking, the king’s castle came into his view. However, as the boy dr
In order to improve English, . A.Jenny’s father bought her a lot of tapes B.Jenny bought a lot of tapes for herself C.a lot of tapes were bought by Jenny D.a lot of tapes wer
—Is that all? —Yes. That’s all _____ I want to take. A. which B. that C. who D. whose
近几年，京津冀等地数城市指数“爆表”，尤其2015年污染最重．为了探究车流量与PM2.5的浓度是否相关，现采集到北方某城市2015年12月份某星期星期一
一个波长范围为150 m—600 m的无线电波波段内，为了避免邻台干扰，两个相邻电台频率至少应差10 kHz，则在此过程中，最多能容纳________个电台。
