VRML是一种模型语言，用来描述一个目标对象如何呈现在_____。
参考答案：Web上（或网上）
Mooring lines should be turned end-for-end occasionally. This is because（）.
A.a line is weakened by constantly pulling on it in one direction
B.normal wear on the line is thus distributed to different areas
C.it prevents the line from kinking or unlaying
D.it prevents permanent misalignment of the line's internal strands
读“以极点为中心的投影图”，回答问题。
写出下列两城市的经纬度位置：
①北京：（），（）；②匹兹堡（），（）。
