选择题
2019 AMC 8 Problem 6: Line of Symmetry
There are 81 grid points (uniformly spaced) in the square shown in the diagram below, including the points on the edges. Point P is in the center of the square. Given that point Q is randomly chosen among the other 80 points, what is the probability that the line PQ is a line of symmetry for the square?
2019 AMC 8 第 6 题：对称线
如下图所示的正方形内有 81 个网格点（均匀分布），包括边缘上的点。 P点位于正方形的中心。假设从其他 80 个点中随机选择点 Q，则线 PQ 是正方形对称线的概率是多少
A.
1/5
B.
1/4
C.
2/5
D.
9/20
E.
1/2