The front of ancient bronze mirrors has flat and concave surface .
古代青铜镜的镜面有平面的，也有凸面的。
A first concave part is formed on the top surface of the base plate.
该基板的该顶表面形成一第一凹陷部。
A second concave part is formed on the bottom surface of the base plate.
该基板的该底表面形成一第二凹陷部。
A second concave part is formed on the bottom surface of the base plate.
该基板的该底表面形成一第二凹陷部。
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