题干
—Did they tell you when to set off?
—No, they didn't.
A：turn back
B：stay inside
C：start out
答案(点此获取答案解析）
C
m，地球的轨道半径为
m，根据你所掌握的物理和天文知识，估算出火星与地球相邻两次距离最小的时间间隔为