on the trail

例句：

1. 1. We're on thetrail of a missing child.
   我们正在追踪一名失踪的孩子。
2. 2. The police are on thetrail of a serial killer.
   警方正在追踪一个连环杀手。
3. 3. He was on the trailof a new business opportunity.
   他在追踪一个新的商业机会。