proof coin

例句：

1. 1. The proof coin was a valuable piece of evidence in the case.
   这个证明硬币是案件中的重要证据。
2. 2.He kept his proof coin hidden in his desk drawer for years.
   他多年来一直把证明硬币藏在他的抽屉里。
3. 3. The museum's exhibit showcased various proof coins from around the world.
   博物馆的展览展示了来自世界各地的各种证明硬币。