a cross-country track的用法和样例：
- A mule is a cross between a horse and an ass.
- On maps, a cross is the symbol for a church.
- Brunch is a cross between breakfast and lunch.
- The priest made a cross over her head.
- I hired a car the day after landing and bought a comprehensive book of maps, which my found most helpful on the cross country.
- Mules are a cross between a horse and an ass.