天文距离单位有哪些?它们各是如何定义的?
参考答案:
天文单位,指日地平均距离;光年,指光在一年内走过的距离;秒差距,指周年视差为1角秒的天体所对应的距离。
If he()my advice, he wouldn't have lost his job.
A. followed
B. should follow
C. had followed
D. would follow
2008年以前的旧版眼保健操一共多少节?