视向速度，径向速度
参考答案：
运动天体靠近或远离地球的速度。
The song is about a couple forced to separate _________, but they valued the memories of their love all their lives.
A．casually
B．permanently
C．temporarily
D．frequently
某单位计算机房失火，应用什么灭火器？为什么？
