A nurse is caring for an 18-month-old toddler who has been hospitalized for 10 days. After the toddler's mother leaves the room, the nurse observes the toddler sitting quietly in the corner of the crib, sucking her thumb. When the nurse approaches the crib, the toddler turns away from the nurse. The nurse should understand that these behaviors indicate which of the following developmental reactions?

A. Developing autonomy is typically associated with increased independence and exploring new skills, not behaviors seen in a distressed or hospitalized child. B. While anxiety may be present, the behavior of turning away and thumb-sucking more strongly suggests regression. C. Resentment toward the mother would not typically result in the described behavior of thumb-sucking and turning away from the nurse. D. Regression is when a child reverts to earlier behaviors, such as thumb-sucking, as a coping mechanism in response to stress or separation from the primary caregiver.