Final answer:
The 18-month-old child has entered the third stage of separation anxiety, where they show signs of detachment, becoming quiet and withdrawn, not the second stage as the question suggests.
Step-by-step explanation:
The behavior exhibited by the 18-month-old client who initially cries and then becomes quiet and withdrawn after the parents leave is indicative of the child having entered the third stage of separation anxiety. During the initial phase, children often protest loudly when they are separated from their caregivers. If the separation continues, they may enter a stage of despair, characterized by less crying and more withdrawal. Finally, the child may enter a stage where they appear to adjust to the separation, showing detachment which includes being quiet and withdrawn, but this is not true adjustment but resignation.
The correct answer to the question is that: b. The child has entered the second stage of separation anxiety. The question seems to have a mistake since the described behavior is actually the third stage.