体重身高相同的甲乙两人,分别用双手握住跨过无摩擦轻滑轮的绳子各一端,他们由初速为零向上爬,经过一定时间,甲相对绳子的速率是乙相对绳子速率的两倍,则到达顶点的情况是:[ C ]
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
免费的网站请分享给朋友吧