a railroad bridge的用法和样例：
- Buildings and debris jam against a railroad bridge over the Cedar River on Saturday in Cedar Rapids, Iowa.
- A railroad bridge damaged by Typhoon Morakot is seen in Taitung, eastern Taiwan August 8, 2009.
- Here is another example illustrating the difference between average and incremental returns: Suppose that a railroad bridge is in urgent need of repair.
- The operation of a railroad needs many men.
- The distance between the two rails of a railroad.