Final answer:
Randy and Lucy concluded that Randy's toy is preferred by observing Julian's spontaneous reactions to both toys, which is a common method used in psychology to assess infants' preferences and behaviors.
Step-by-step explanation:
Randy and Lucy have both purchased toys for their new baby cousin, Julian. To determine which toy Julian prefers, they present both toys to him at the same time and observe his reaction. The answer to the question of how they came to the conclusion that Randy's toy is preferred over Lucy's would be B) Observing Julian's spontaneous reactions to each toy. This method is a form of structured observation, similar to those used in psychological studies to understand infant behavior and preferences. For instance, Mary Ainsworth's Strange Situation experiment observed infants' reactions to assess attachment styles with caregivers. Here, Randy and Lucy are looking for which toy Julian chooses to engage with or shows more positive reactions towards, a clear indicator of his preference.