**Core Concept:**
The question is asking about the developmental milestones of a baby, specifically mouthing behavior, stranger anxiety, likes and dislikes for food, and the most appropriate age for these behaviors. These developmental milestones are part of a child's psychosocial development and are essential for understanding a child's growth and progress.

**Why the Correct Answer is Right:**
The correct answer, **C. 6 months**, is chosen because it represents a typical age when babies exhibit these developmental milestones. At around 6 months, babies begin to explore their environment through mouthing behavior, also known as oral exploration or oral motor exploration. They start to develop a preference for certain tastes and textures of food, which is referred to as likes and dislikes for food.

Stranger anxiety is a key psychosocial milestone that usually emerges around 6 months of age, where babies become anxious and fearful when presented with unfamiliar people, objects, or situations. This anxiety is a normal part of their development and helps to protect them from potential harm.

**Why Each Wrong Option is Incorrect:**
A) **3 months:** While babies might exhibit some form of exploration around this age, they are generally too young to demonstrate oral motor skills, likes and dislikes for food, and stranger anxiety.

B) **9 months:** Although some babies might exhibit stranger anxiety around this age, the development of oral motor skills, likes and dislikes for food, and the ability to express preferences are generally observed later, around 6 months.

D) **12 months:** While babies might show some signs of stranger anxiety and preferences around this age, they are still too young to exhibit the complex behaviors of mouthing, likes and dislikes for food, and stranger anxiety in a typical 6-month-old baby.

**Clinical Pearl:**
The concept of "stranger anxiety" is crucial for parents and caregivers to understand as it helps them to create a safe environment for the child, ensuring they are protected from potential harm while also allowing them to explore and develop normally. By providing a supportive and stimulating environment, babies can reach their developmental milestones more easily.