Final answer:
Teens may be more easily distracted by rewards than adults and knowing about a reward beforehand could reduce their intrinsic motivation, leading to a focus on extrinsic motivation. (option B)
Step-by-step explanation:
The findings of Roper's experiment are not detailed in the question, but based on the context provided regarding teen behavior, reward expectation, and motivation, we can infer general concepts about adolescent psychology. Adolescents may take more risks than adults even though they can evaluate risks and rewards similarly due to different values, possible higher weight given to immediate rewards, or differential brain development stages affecting their impulse control. If teens knew about the reward before participating in a study, it could affect their behavior by diminishing their intrinsic motivation, as knowing about a reward can shift focus to extrinsic motivation.
In the context of the experiment, option C suggesting that teens are more easily distracted, even when they don't gain a reward, appears to be the most plausible, aligning with the broader understanding that teens and adults may value and respond to rewards differently. This response is informed by the information on how tangible and intangible rewards can affect motivation and by previous research mentioned, such as the study by Mischel et al.