Final answer:
The correct answer is option a. Is forming specific attachments to familiar caregivers.
Step-by-step explanation:
At 4 months old, Maisie is in the early stages of development with regard to attachment and cognitive milestones. Given her age, Maisie is forming specific attachments to familiar caregivers, a process that evolves as infants spend more time and experience consistent care from particular individuals. It is a bit early for her to show signs of stranger anxiety or to demonstrate object permanence, as these typically emerge around 6 and 8 months respectively.
The ability to engage in joint attention, which is crucial for language learning and social interaction, tends to develop later in infancy.