题目

He ______ his paper to see if there are any obvious mistakes. A. looked into        B. looked up          C. looked around           D. looked through 答案：D如图所示，绳系卫星系在航天器上方，航天飞机进行适当调控后关闭发动机，它们一起在赤道上空绕地球作匀速圆周运动（绳长不可忽略）．下列说法正确的是（　　）A．长绳中一定没有弹力B．卫星只能在航天飞机的正上方C．绳系卫星的加速度比航天器的大D．若连接它们的长绳突然断了，卫星将做离心运动