What is the most suitable word that describes the work of a policeman according to the passage

A．he must work hard to help reform criminals
B．he must believe as professional lawyers do
C．he must be able to tell when and where a crime is committed
D．he must justify the arrests he makes of criminals

A．patrolling the street, rain or shine
B．tracking and arresting criminals
C．collecting and providing evidence
D．consulting the rules of law