Lyle is studying alone late Friday night in the almost deserted library. His concentration is interrupted when he notices another student nearby slumped over his desk, making sounds that suggest he might be in pain. In this situation, it is very likely that Lyle will engage in _, because he is NOT constrained by _.

The instructions in the question make it clear that Lyle is in an almost deserted library. The reason why that fact was mentioned is because the presence of many people influences the general behavior. People tend to not help someone in need when there are other bystanders. The greater the number of bystanders, the less likely a person is to offer help. The bystander effect was popularized by social psychologists Bibb Latané and John Darley after a woman was stabbed to death in front of her apartment in New York. None of her neighbors tried to intervene and help. One explanation to such inertia is that people observe those around them to decide how to act. If no one is helping, they choose not to help as well.

Prosocial behavior, on the other hand, is altruistic. It is a behavior that benefits others and society as a whole. Lyle is not constrained by the bystander effect. For that reason, he will show prosocial behavior by helping the student who seems to be in pain.