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 when toddlers strive for independence in doing tasks. However, the observed behavior indicates distress rather than independence. B. Resentment toward the mother is not typical of toddlers in response to separation. Toddlers at this age may feel anxious, but they do not typically express complex emotions like resentment. C. Regression is possible in a hospitalized child, as they might revert to behaviors from earlier developmental stages, but the described behavior aligns more closely with separation anxiety. D. Separation anxiety is a normal developmental stage for toddlers, especially when they are separated from their primary caregiver. The behaviors of turning away and thumb-sucking are common signs of distress due to separation from the mother.