Final answer:
Joshua is experiencing separation anxiety.
Step-by-step explanation:
Based on the information provided, it seems that option c. Joshua is experiencing separation anxiety is the most appropriate answer. Separation anxiety is a common reaction that infants and toddlers experience when they are separated from their main caregiver. Joshua's discomfort when picked up by other adults suggests that he is strongly attached to his dad and feels uncomfortable when he is not near him. This behavior is typical of separation anxiety.