a police force的用法和样例：
- A woman who is a member of a police force.
- A man who is a member of a police force.
- A person,usually a member of a police force,who investigates crimes and obtains evidence or information.
- A vigilant police force helps to control crime.
- Station, The headquarters of a unit of a police force, swheresthose under arrest are first charged.
- The London police force is headed by a commissioner.