Final answer:
The Strange Situation is the procedure developed by Mary Ainsworth to study the varying attachment styles between caregivers and infants, identifying secure, avoidant, resistant, and disorganized as the four styles. During this procedure, critical insight into attachment is gained when observing the child's reaction upon the caregiver's return.
Step-by-step explanation:
Mary Ainsworth used an experimental procedure known as the Strange Situation to study the attachment styles between infants and their caregivers. In this structured observational research, various phases were employed such as a stranger entering the room, the caregiver leaving, and then returning to see how the infant reacts, with the key phase focusing on the reunion of caregiver and infant which elucidates the attachment style. Ainsworth identified four attachment styles: secure, avoidant, resistant, and disorganized. Secure attachment is characterized by the child's distress during caregiver's absence and happiness upon their return, using the caregiver as a secure base to explore from and seek comfort in times of stress.
In this context, secure attachment is demonstrated when the child uses the caregiver as a safe base from which to explore, which is the final answer to the student's question regarding attachment styles in the Strange Situation (Option a).