a single firer的用法和样例：
- The letter was written on a single sheet of paper.
- It was a massive anti-matter annihilator cannon, capable of destroying entire worlds at a single firing.
- He got over the stream with a single leap.
- The bridge crosses the river in a single span.
- Do you want a single or a return ticket?
- The huntsman fired a single shot at the lion and settled its hash.