Okay, let me tackle this question. The question is about a child's fear of strangers and separation from parents. The options are missing, but the correct answer is supposed to be something that diminishes these fears.

First, I need to recall the developmental stages. Around 6-12 months, infants develop stranger anxiety and separation anxiety. This is part of normal development. So the question is asking what would reduce these fears.

The core concept here is probably related to developmental psychology. The answer might be related to the child's growing cognitive abilities, like object permanence. Jean Piaget's stages of development come to mind. In the sensorimotor stage, object permanence develops around 8-12 months, which helps the child understand that the parent still exists even when out of sight, reducing separation anxiety.

So the correct answer would be something like "Development of object permanence." Let's check the options. If option C is that, then it's correct. The other options might be things like increased motor skills, language development, or social referencing, which are not directly related to reducing these specific fears. For example, social referencing (option A) might actually increase fear by making the child more aware of others' reactions. Language development (option B) could help later but isn't the primary factor here. Secure attachment (option D) is important but is more about the parent-child relationship rather than the mechanism that reduces the fear itself.

Clinical pearl: Object permanence is a key milestone in reducing separation anxiety. Remember Piaget's stages for similar questions.

**Core Concept**
Stranger and separation anxiety in children aged 6–12 months are rooted in **object permanence**—the understanding that objects (or people) exist even when out of sight. This developmental milestone, described by Piaget, reduces anxiety by allowing children to internalize the parent’s presence during separation.

**Why the Correct Answer is Right**
**Object permanence** (Option C) enables children to mentally represent their caregivers, reducing fear during separation. Before this milestone, the child cannot grasp the parent’s continued existence when absent, heightening anxiety. As object permanence develops, the child gains confidence that the parent will return, alleviating both separation and stranger fear.

**Why Each Wrong Option is Incorrect**
**Option A: Social referencing** (observing others’ reactions to strangers) *increases* awareness of potential threats, potentially *heightening* fear.
**Option B: Motor skill development** (e.g., crawling) expands exploration but does not directly address the cognitive basis of anxiety.
**Option D: Secure attachment** is foundational but refers to the quality of the parent-child bond, not the cognitive milestone reducing fear.

**Clinical Pearl / High-Yield Fact**
**Object permanence** is a key milestone in Piaget’s sensorimotor stage (8–12 months). Remember: “Out of sight, out of mind” applies to infants *before* object permanence develops. This concept is frequently tested in pediatric development questions.

**Correct Answer: C. Development of object permanence**

✓ Correct Answer: C. Third Birthday