单项选择题

"Block patrol (巡逻，巡逻队)," "community watch" "civilian patrol. "
They may have different names in different cities across the country but they all are civilian volunteer groups that help police department in major metropolitan (大城市的) areas. In the volunteer groups, men and women are trained by local police to watch for potential trouble in their neighborhood. Spotting a suspicious looking vehicle or person can help police to fight crime in the neighborhood.
Aside from keeping an eye on the neighborhood, volunteers often perform other duties. Civilian volunteers may work at parades or other types of gatherings, freeing the police to do their main job—catching criminals. Volunteers in some cities also conduct surveys to make people aware of ways that they can protect themselves from being crime victims. Some volunteers help people to engrave identification numbers on their personal property. Such a number would make the retrieval (追回) of a stolen item easier. Other volunteers watch children who may need help going to and from school.
If you are interested in becoming a part of the volunteer group in your area, contact your local police department. The author is primarily concerned with ______.