最外层
the most external of several layers of a substance or material
物质或材料的几个层次中最外的一层
the farthest point or line from the center
最外环
the most external of a series of concentric rings
一系列同心环中最外面的一个
最远的范围
the farthest extent or limit of something
某事物最远的范围或极限