运动员在长跑后因流汗过多常出现抽搐现象，这是因为身体中哪种物质的含量低导致的（    ）

图为某种鱼饵自动投放器中的投饵管装置示意图，其下半部AB是一长为2R的竖直细管，上半部BC是半径为R的四分之一圆弧弯管，管口沿水平方向，AB管内有一原长为R、下端固定的轻质弹簧．投饵时，每次总将弹簧长度压缩到0.5R后锁定，在弹簧上端放置一粒鱼饵，解除锁定，弹簧可将鱼饵弹射出去．设质量为m的鱼饵到达管口C时，对管壁的作用力恰好为零．不计鱼饵在运动过程中的机械能损失，且锁定和解除锁定时，均不改变弹簧的弹性势能．已知重力加速度为g．求：

***曾称赞傅作义是“民族功臣”，“为和平解决各地战事问题和减轻人民的痛苦树立了榜样。”上述评价和哪次战役有关（    ）

    Mr. Brown is a teacher. He is from New York, America. He would like（想）to work in China because he likes our country. He thinks Chinese people are very friendly and he likes to live in China. He is happy to work in our school. He likes the school life here. He teaches English. There are 50 students in his class. Mr. Brown is kind. He and his students are good friends, too.
    Now some of Mr. Brown's students play sports on the playground（操场）. Bill and Mike play tennis. Tom and John play ping-pong. The other students play basketball. Mr. Brown is happy to play basketball with them. They have a good time.
阅读上面的短文，根据短文内容，选择最佳选项。   

已知向量，，，且，则的值分别为