语法总结
过去完成时与一般过去时
had put、had never thought 表示在 received 之前已经发生的动作。
相似句：
- She had left before I arrived.
- They had finished when we called.
will 表示将来结果
决定改用邮局后，Letters will cost... / will travel... 说明将来的结果。
相似句：
- The trip will take two hours.
- This road will save time.