In Order to Reduce Risky Behavior of Children on a Playground

In order to reduce risky behavior of children on a playground, a safety officer offered rewards to the entire class if everyone played more safely. Researchers found this program

A) effective, even though the reinforcements were very small (e.g., blue ribbons) .
B) effective, provided the reinforcements were very large (e.g., $5 per week) .
C) effective, but only on the day the reinforcement was delivered.
D) less effective than physically punishing children for risky behavior.