The subsolar point will cross every latitude between these two extremes exactly twice per year.
太阳直射点每年恰好两次穿越这两个极端之间的所有纬度。
2
As anyone who has done any cross-country hiking will tell you, there are two data points which must be in-hand before a course can be plotted: the starting point and the ending point.
如同所有完成过越野徒步旅行的人告诉您的，在绘制行程之前必须掌握两个数据点：出发点和终点。
3
A two-dimensional model of such a universe would look like a sphere. It's impossible to have parallel geodesics (straight lines on a curved surface) — the two lines will cross at some point.