Apolice officer visits ms. duhaime's first-grade class one morning to talk about safety precautions at home and on the street. the students listen quietly and attentively while the officer speaks. at the end of the visit, the officer and teacher agree that the students' good behavior warrants some kind of reinforcement. given what we know about effective reinforcers at different grade levels, their best choice would be:
a) plastic toy police "badges" awarded by the officer. b) a letter home to parents describing the children's good behavior. c) an official-looking "good behavior" certificate given at the school's award ceremony the following week. d) twenty minutes of free time at the end of the day.