资料题：The“truants" referred to in line 11 are（　）。

Few institutions are more important to an urban community than its police, yet there are few subjects historians know so little about.Most of the early academic interest developed among political scientists and sociologists, who usually examined their own contemporary problems with only a nod toward the past.Even the public seemed concerned only during crime waves, periods of blatant corruption, or after a particularly grisly episode.Party regulars and reformers generally viewed the institution from a political perspective;newspapers and magazines-the nineteenth century media emphasized the vivid and spectacular.Yet urban society has always vested a wide,indeed awesome, responsibility in its police.Not only were they to maintain order, prevent crime, and protect life and property, but historically they were also to fight fires, suppress vice, assist in health services, supervise elections, direct traffic, inspect buildings, and locate truants and runaways.In addition, it was assumed that the police were the special guardians of :the citizens' liberties and the community'stranquility.Of course, the performance never matched expectations.The record contains some success, but mostly failure;some effective leadership, but largely official incompetence and betrayal.The notion of a professional police force in America is a creation of the twentieth century; not until our own time have cities begun to take the steps necessary to produce modem departments.