a police helicopter的用法和样例：
- A police helicopter was launched to search for the killer, who is believed to be heavily bloodstained.
- A family and three aircrew escaped unhurt after a police helicopter spun out of the sky and crashed through the roof of a house in Cardiff.
- A police patrol boat hailed to us to come to.
- A police car jogged along on the rough path to the village.
- The thieves were caught in a police trap.